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]: Carbon forms ____ bonds.\Question: Choose the right answer from options given a) five b) four c) two d) three
[EX A]: b

[EX Q]: Cats can harbor a heartworm infection at any age from ____ months to seventeen years.\Question: Choose the right answer from options given a) one b) six c) nine d) three
[EX A]: c

[EX Q]: Unipolar motors have ____ coils and are likely to have five or six wires attached.\Question: Choose the right answer from options given a) one b) two c) eight d) four
[EX A]:
d