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:
Fruit trees are usually safe after ____ years.\Question: Choose the right answer from options given a) five b) four c) no d) three

Ex Output:
d


Ex Input:
Stable oxygen has eight protons and ____ neutrons.\Question: Choose the right answer from options given a) eight b) ten c) three d) zero

Ex Output:
a


Ex Input:
Refraction occurs ____ times, as the light intersects the vessel s inner and outer surfaces .\Question: Choose the right answer from options given a) eight b) seven c) six d) four

Ex Output:

d