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:
Atoms are extremely small, on the order of a few ____ billionths of a meter.\Question: Choose the right answer from options given a) ten b) seven c) nine d) eight

Ex Output:
a


Ex Input:
Cows have four stomachs, and the first ____ yield merchantable tripe.\Question: Choose the right answer from options given a) two b) five c) zero d) three

Ex Output:
d


Ex Input:
Porcupines have ____ toes on their front paws and five on their rear paws.\Question: Choose the right answer from options given a) one b) five c) six d) four

Ex Output:

d