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: Many comets have ____ tails.\Question: Choose the right answer from options given a) two b) six c) three d) one

Output: a


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: Northern krill go through ____ larval stages after hatching.\Question: Choose the right answer from options given a) ten b) four c) one d) seven


Output: b