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: Routers are basically systems, which connect ____ networks together.\Question: Choose the right answer from options given a) three b) two c) nine d) six
Example Output: b

Example Input: Many animals use two or ____ forest structure types.\Question: Choose the right answer from options given a) eight b) zero c) two d) three
Example Output: d

Example Input: Veterinarians divide stringhalt into ____ major categories.\Question: Choose the right answer from options given a) seven b) two c) ten d) five
Example Output:
b