Emily is riding her bicycle. Which best explains why only some of the energy used to pedal her bicycle is transferred into forward motion of the bicycle? OPTIONS:
- The energy of the bicycle tire is applied in a circular motion.
- The energy of the bicycle is transferred to only one wheel.
- The gears and chain of the bicycle are covered with oil.
- The gears and chain of the bicycle generate friction.
A: The gears and chain of the bicycle generate friction.

A student is measuring the boiling point of a salt and water mixture. He takes one temperature measurement of 105°C. Which is the best way to ensure the results are valid? OPTIONS:
- repeat the investigation
- change the volume of water
- add more salt to the mixture
- do the investigation without salt
A: repeat the investigation

Which simple machine increases the distance over which a load travels and reduces the needed force? OPTIONS:
- wheel and axle
- wedge
- pulley
- inclined plane
A: inclined plane

In a grassland ecosystem, organisms of the same species eat the same food. When there is a lack of rain, which is most likely increased? OPTIONS:
- carrying capacity
- population density
- competition for space
- competition for resources
A:
competition for resources