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: Young emus are very vulnerable to disease until they are about ____ months old.\Question: Choose the right answer from options given a) no b) ten c) six d) three
Example Output: d

Example Input: Springtails reproduce quickly usually within three to ____ weeks.\Question: Choose the right answer from options given a) five b) six c) nine d) three
Example Output: a

Example Input: Bacteria are prokaryotic because they have ____ nucleus or membrane-bound organelles.\Question: Choose the right answer from options given a) three b) no c) zero d) four
Example Output:
b