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: Human rabies is extremely rare, and there have been no cases in Oregon in the last ____ years.\Question: Choose the right answer from options given a) nine b) five c) ten d) eight
Example Output: d

Example Input: Young children suffer from an average of six to ____ colds a year.\Question: Choose the right answer from options given a) ten b) eight c) two d) one
Example Output: b

Example Input: Hatchlings fall into ____ main categories, nidicolous and nidifugous.\Question: Choose the right answer from options given a) nine b) zero c) one d) two
Example Output:
d