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:
ATMs are expensive machines with an average useful life of ____ to fifteen years.\Question: Choose the right answer from options given a) nine b) eight c) ten d) two

Ex Output:
c


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:
Flagella consist of ____ parallel protein fibers intertwined into a triple helical structure.\Question: Choose the right answer from options given a) eight b) five c) zero d) three

Ex Output:

d