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:
Perennial grass takes three to ____ years before it is mature enough to produce adequate seed.\Question: Choose the right answer from options given a) five b) seven c) six d) four

Ex Output:
a


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:
Heatstroke occurs in ____ forms, exertional and classic.\Question: Choose the right answer from options given a) one b) six c) eight d) two

Ex Output:

d