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: National forests have regulations that restrict ____ wheeler use to established roads.\Question: Choose the right answer from options given a) no b) four c) six d) nine
Example Output: b

Example Input: Most gerbils live three to ____ years and have few health problems.\Question: Choose the right answer from options given a) three b) four c) seven d) zero
Example Output: b

Example Input: Ethernet is a mode of electronic communication that is at least ____ times faster than a modem.\Question: Choose the right answer from options given a) no b) ten c) nine d) five
Example Output:
b