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: Pneumatic motor is a six-point unit with ____ pneumatics facing up and three facing down.\Question: Choose the right answer from options given a) five b) no c) three d) nine
Example Output: c

Example Input: Scientists divide bats into ____ groups.\Question: Choose the right answer from options given a) five b) two c) one d) zero
Example Output: b

Example Input: Colorectal cancer begins with ____ symptoms at all.\Question: Choose the right answer from options given a) nine b) no c) six d) zero
Example Output:
b