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:
Ocular dryness responds to the use of artificial tears applied every ____ to three hours.\Question: Choose the right answer from options given a) no b) one c) three d) eight

Ex Output:
b


Ex Input:
Human malaria is caused by ____ species of Plasmodium . .\Question: Choose the right answer from options given a) six b) ten c) seven d) four

Ex Output:
d


Ex Input:
ClamShells produce a soap with a completely smooth top - ____ indentations of any kind.\Question: Choose the right answer from options given a) no b) three c) ten d) two

Ex Output:

a