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: Most viruses have only ____ organelles.\Question: Choose the right answer from options given a) ten b) two c) four d) eight
Example Output: b

Example Input: Young squirrels remain in the nest for about ____ weeks.\Question: Choose the right answer from options given a) seven b) six c) two d) eight
Example Output: b

Example Input: Sexual reproduction requires the presence of ____ mating types.\Question: Choose the right answer from options given a) four b) no c) three d) two
Example Output:
d