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: Some experts believe whining peaks around the ages of ____ or four.\Question: Choose the right answer from options given a) three b) no c) four d) seven
Example Output: a

Example Input: Teething begins for most babies around ____ to six months.\Question: Choose the right answer from options given a) three b) four c) five d) seven
Example Output: b

Example Input: Angiosperms inhabit all ____ continents, as well as the oceans.\Question: Choose the right answer from options given a) five b) seven c) three d) zero
Example Output:
b