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:
Trains kill ____ people every year.\Question: Choose the right answer from options given a) zero b) three c) no d) four

Ex Output:
d


Ex Input:
Right whales are slow swimmers, averaging just ____ miles per hour.\Question: Choose the right answer from options given a) nine b) six c) two d) five

Ex Output:
b


Ex Input:
Oxygen exists in all ____ allotropic forms.\Question: Choose the right answer from options given a) three b) two c) nine d) six

Ex Output:

a