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: Ozone is a naturally occurring molecule containing ____ atoms of oxygen.\Question: Choose the right answer from options given a) three b) five c) nine d) eight
Example Output: a

Example Input: Mechanical stability comes from having fused quartz, in ____ gravity, cold.\Question: Choose the right answer from options given a) five b) zero c) six d) two
Example Output: b

Example Input: Cnidarians are essentially bags made of ____ cell layers.\Question: Choose the right answer from options given a) zero b) seven c) four d) two
Example Output:
d