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 Q]: Scientists divide bats into ____ groups.\Question: Choose the right answer from options given a) five b) two c) one d) zero
[EX A]: b

[EX Q]: Wolverines reproduce every ____ or three years.\Question: Choose the right answer from options given a) two b) three c) one d) four
[EX A]: a

[EX Q]: Phosphoric acid contains ____ hydrogen ions.\Question: Choose the right answer from options given a) six b) three c) two d) no
[EX A]:
b