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: Rheumatic fever begins one to ____ weeks after an untreated streptococcal infection.\Question: Choose the right answer from options given a) six b) ten c) two d) zero
Example Output: a

Example Input: Iron comes in ____ forms.\Question: Choose the right answer from options given a) one b) eight c) two d) seven
Example Output:
c