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:
Molecules are ____ or more atoms stuck together.\Question: Choose the right answer from options given a) two b) zero c) six d) eight

Ex Output:
a


Ex Input:
Scientists divide bats into ____ groups.\Question: Choose the right answer from options given a) five b) two c) one d) zero

Ex Output:
b


Ex Input:
Particle sizes extend from the nanometer range over more than ____ orders of magnitude.\Question: Choose the right answer from options given a) nine b) one c) four d) zero

Ex Output:

c