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: Chimeras are ____ headed creatures that shoot fire from all three heads, damaging a wide area.\Question: Choose the right answer from options given a) three b) one c) eight d) six
Example Output: a

Example Input: Cows can be up to ____ times more active than normal while in heat.\Question: Choose the right answer from options given a) eight b) nine c) two d) six
Example Output: a

Example Input: Oxygen atoms can have ____ different masses, known as isotopes.\Question: Choose the right answer from options given a) one b) three c) eight d) five
Example Output:
b