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: Infants can tell their mothers from other mothers in ____ days.\Question: Choose the right answer from options given a) no b) zero c) five d) three
Example Output: d

Example Input: Chitons have a shell composed of ____ separate shell plates or valves .\Question: Choose the right answer from options given a) ten b) six c) eight d) zero
Example Output:
c