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:
Water is the only natural substance which exists in all ____ states of matter in nature.\Question: Choose the right answer from options given a) no b) eight c) six d) three

Ex Output:
d


Ex Input:
Copper is ____ times higher in dog liver than in human liver.\Question: Choose the right answer from options given a) three b) ten c) six d) one

Ex Output:
b


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

Ex Output:

d