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: Calves can browse and follow their mother at three weeks old and are weaned at ____ months.\Question: Choose the right answer from options given a) five b) seven c) four d) three
Example Output: a

Example Input: Astronomical observations suggest ____ or close to zero space-time curvature.\Question: Choose the right answer from options given a) six b) zero c) ten d) seven
Example Output: b

Example Input: Triple bonds are ____ lines.\Question: Choose the right answer from options given a) nine b) three c) zero d) six
Example Output:
b