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').

Ex Input:
Antibodies contain ____ pairs of protein chains.\Question: Choose the right answer from options given a) no b) two c) nine d) zero

Ex Output:
b


Ex Input:
Some olive trees live to be ____ thousand years old.\Question: Choose the right answer from options given a) ten b) zero c) two d) seven

Ex Output:
c


Ex Input:
Gravity is the force that brings ____ objects together .\Question: Choose the right answer from options given a) five b) two c) one d) nine

Ex Output:

b