Part 1. Definition
You are given a paragraph, a question and some answer options (associated with "A", "B", "C", "D", etc.) You need to list all the correct answer options with their associated letters (e.g. "A" can be a valid answer). Note that sometimes, more than one option can answer the question correctly and completely. In those cases, please generate all such options separated by a comma (e.g. "A, B" is a valid answer). Do not generate anything else apart from one or more of the following characters: 'A', 'B, 'C', 'D', etc.
Part 2. Example
Paragraph- Sent 1: Obama was born on August 4, 1961, at Kapiʻolani Maternity & Gynecological Hospital in Honolulu, Hawaii.
Sent 2: He is the only President to have been born in Hawaii.
Sent 3: He was born to a white mother and a black father.
Sent 4: His mother, Ann Dunham (1942-1995), was born in Wichita, Kansas, of mostly English descent, with some German, Irish, Scottish, Swiss, and Welsh ancestry. Question: How old was Obama's mother when he was born? (A) teenager (B) in his 40s (C) mid 20s (D) almost twenty.
Answer: D.
Explanation: Obama was born in 1961. His mother was born in 1942 and 1961-1942=19. Therefore, "almost twenty" answers the question sufficiently.
Part 3. Exercise
Paragraph- Sent 1: Duane was hungry, but he hurried through the ample supper that was set before him, urged on by curiosity and astonishment.
Sent 2: The only way he could account for his presence there in a ranger's camp was that MacNelly hoped to get useful information out of him.
Sent 3: Still that would hardly have made this captain so eager.
Sent 4: There was a mystery here, and Duane could scarcely wait for it to be solved.
Sent 5: While eating he had bent keen eyes around him.
Sent 6: After a first quiet scrutiny the rangers apparently paid no more attention to him.
Sent 7: They were all veterans in service--Duane saw that--and rugged, powerful men of iron constitution.
Sent 8: Despite the occasional joke and sally of the more youthful members, and a general conversation of camp-fire nature, Duane was not deceived about the fact that his advent had been an unusual and striking one, which had caused an undercurrent of conjecture and even consternation among them.
Sent 9: These rangers were too well trained to appear openly curious about their captain's guest.
Sent 10: If they had not deliberately attempted to be oblivious of his presence Duane would have concluded they thought him an ordinary visitor, somehow of use to MacNelly.
Sent 11: As it was, Duane felt a suspense that must have been due to a hint of his identity. 
Question: Who invited Duane to stay at the camp? (A) The Rangers (B) MacNelly (C) Veterans.
Answer:
B.