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:
Waves can sometimes reach ____ feet tall, while still being playful and fun.\Question: Choose the right answer from options given a) nine b) eight c) ten d) no

Ex Output:
c


Ex Input:
Astronomical observations suggest ____ or close to zero space-time curvature.\Question: Choose the right answer from options given a) six b) zero c) ten d) seven

Ex Output:
b


Ex Input:
Many scientists believe the neutrino has ____ mass at all.\Question: Choose the right answer from options given a) eight b) zero c) two d) no

Ex Output:

d