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: Embryos develop and hatch in about four weeks, then spend four to ____ months in the tadpole stage.\Question: Choose the right answer from options given a) five b) nine c) eight d) two
Example Output: a

Example Input: Insects have ____ common types of metamorphosis.\Question: Choose the right answer from options given a) six b) eight c) two d) seven
Example Output: c

Example Input: Vitamin E comes in ____ forms.\Question: Choose the right answer from options given a) eight b) three c) two d) zero
Example Output:
b