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:
Snowflakes are crystals that have many different shapes, but each snowflake has ____ points on it.\Question: Choose the right answer from options given a) six b) nine c) one d) seven

Ex Output:
a


Ex Input:
Brachiopods are superficially similar to bivalves, both having ____ shells.\Question: Choose the right answer from options given a) two b) eight c) seven d) one

Ex Output:
a


Ex Input:
Massless particles have ____ rest mass.\Question: Choose the right answer from options given a) two b) zero c) five d) one

Ex Output:

b