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').

Input: Consider Input: Background radiation comes from ____ sources.\Question: Choose the right answer from options given a) zero b) three c) four d) no

Output: b


Input: Consider Input: Some male fish return after just ____ years.\Question: Choose the right answer from options given a) no b) two c) one d) six

Output: b


Input: Consider Input: Many bacteria have plasmids with ____ obvious function.\Question: Choose the right answer from options given a) nine b) eight c) two d) no


Output: d