Given a sentence with a missing word, pick the answer option that best fills out the missing word in the sentence. Indicate each answer with its index ('a', 'b', 'c', 'd').

Example Input: Astronauts sleep only ____ hours each night, on average.\Question: Choose the right answer from options given a) six b) one c) four d) seven
Example Output: a

Example Input: Copper is ____ times higher in dog liver than in human liver.\Question: Choose the right answer from options given a) three b) ten c) six d) one
Example Output: b

Example Input: Most lemmings are three to six inches in length and weigh less than ____ ounces.\Question: Choose the right answer from options given a) ten b) four c) two d) no
Example Output:
b