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:
Respiratory therapists complete ____ to four years of education.\Question: Choose the right answer from options given a) one b) nine c) zero d) two

Ex Output:
d


Ex Input:
Most marine sediments are of ____ basic types.\Question: Choose the right answer from options given a) three b) ten c) two d) nine

Ex Output:
c


Ex Input:
Carbon is electron deficient - it only has ____ electrons around it.\Question: Choose the right answer from options given a) seven b) eight c) nine d) four

Ex Output:

d