It takes two to duet  , and one question for scientists is how these coordinated   performances arise -- in birds. Are they the result of cooperation, a way in which one pair signals to others that they've got it together? Or are they the result of conflict, evolving to avoid one partner's song interfering with the other's? A study of duetting in Peruvian warbling antbirds  suggests that it might be a little of both, and that context is everything. Joseph A. Tobias and Nathalie Seddon of the University of Oxford show in Current Biology that sexual conflict can cause the female of a pair that normally cooperates to "jam" the male's song by singing over it. The researchers exposed antbird pairs to recorded songs of other antbirds and monitored the songs the pairs produced. In one experiment, they played the songs of an intruding pair. In this case, the resident pair "both are likely to lose their territory, so both should cooperate," Dr. Tobias said. And they do. They produce a coordinated duet that in effect tells the intruders to keep away. But when the researchers played the song of a single female, the pair behaved differently. "You'd expect the resident female to be highly motivated to defend her position in the partnership," Dr. Tobias said. And that's what occurs. The male sings its heart out, flirting  with the single female, and the female of the pair does its best to interfere with the song by singing over it, apparently to make her mate less attractive to the other female. "It's clear that the male doesn't like what she's doing," Dr. Tobias said. The behavior "breaks up what is otherwise a very cooperative situation into a more complicated signal," he added. It's the first evidence of this kind of signal jamming among pairs, Dr. Tobias said. And in that it leads the male to alter its song to avoid the female's interfering notes, it shows that this kind of conflict could, over a long period, drive the evolution of coordinated song. How did the researchers conduct the experiment? A) They put the antbird pairs back to nature and observe them. B) They played different recorded songs of other antbirds. C) They put an antbird to the other's territory and observed. D) They played the songs of an intruding pair.
B


(Question)
I was fortunate to begin my day camp career at Ramaquois as a four-year-old in 1984. I can clearly remember my first bus ride to camp, sitting next to my older sister. Stepping out of the bus, and into a new, strange world, there was no way I could comprehend how important that moment was for me. Ramaquois would become my summer home until this day.     My first summer at day camp was definitely a new experience for me. I had never had a "bunk  " or a "cubby  " before. My counselors   sort of reminded me of my pre-school teachers, but they were...different somehow... I didn't usually enjoy new things and I was slow to warm up to camp. From what my parents tell me, my counselors were very patient with me. When I needed a friend, a counselor was there. When I needed words of encouragement, they got into conversation with me. When I was too shy to ask, they offered help.               I don't remember the specific moment when things changed, but I know that at some point that summer, things just became different. I couldn't wait for the bus to arrive in the morning. I feared the weekends. And on the last day of camp, I cried--just like the first day. I was attracted. Ramaquois was a part of my life.                I spent 11 summers as a camper at Ramaquois. I had no idea that those summers were just the beginning. I remained at camp for seven years as a counselor, five years a division leader and now I am lucky enough to be an assistant director working with the most unique and talented administrative team in the summer camp industry. I am one of the lucky people that truly enjoys going to work each and every day. From the test, we know that the day camp   _  . A) was organized by pre-school teachers. B) gave children something to do together with their parents. C) operated Monday through Friday D) was close to the author's home
(Answer)
C


I was in Houston a few weeks ago,and needed to be back home in Austin by midmorning the next day.Though I usually left in the evening,for some reason last time I had to choose to set off after midnight. I was on my way back to Austin when I realized I left an important file,and knew I had to return to get it.I took the first exit I could,but when I rounded the corner,an 18-wheeler was stopped dead in the exit lane.I swerved  to avoid it,and then I realized that there was something wrong with my car.So I pulled into a small parking lot and unsurprisingly found the area deserted at 3:15am.I've lived in urban areas most of my life.I'm fairly street-wise and don't become frightened easily,but I knew I was in a pretty tough neighborhood. There was no one in Houston to pick me up.I immediately locked the doors and picked up my phone to call a tow truck.Soon a young man knocked on my driver's side window and asked if he could help me.Judging from his appearance,he was far from a mad man,but I knew he was far more likely to rob than help me.So I lied to him.After a while,he asked again,but this time I politely refused and told him the tow truck was due any minute.He finally said,"Madam,you need help.A tow truck in Houston will arrive anywhere between 45minutes and approximately never (which I knew was true),and you aren't going anywhere until you change your flat tire." After considering thoroughly,I got out.He looked surprised,but got right to work.He changed the tire,returned the seat to its place and said,"Thank you for letting me help you.You gave me a chance when most people would never open the door to someone like me.Would it be okay if I gave you a hug?"When I recovered,I gave him a giant hug.I left with a new tire and a renewed faith in human nature. What's the matter with the author's car? A) It couldn't get started. B) Its oil ran out. C) It was out of control. D) Its tire blew out.

D