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: Sexual maturity occurs at three to four years for females and ____ to five years for males.\Question: Choose the right answer from options given a) nine b) seven c) five d) four
Example Output: d

Example Input: Nymphs feed and mature through ____ instars in about six to eight weeks.\Question: Choose the right answer from options given a) four b) eight c) five d) no
Example Output: c

Example Input: Some insects go through ____ metamorphosis at all.\Question: Choose the right answer from options given a) no b) two c) seven d) four
Example Output:
a