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]: Rock cavies become sexually mature when they are about one to ____ months old.\Question: Choose the right answer from options given a) one b) four c) three d) seven
[EX A]: c

[EX Q]: Teething begins for most babies around ____ to six months.\Question: Choose the right answer from options given a) three b) four c) five d) seven
[EX A]: b

[EX Q]: Chlorine has ____ naturally occurring isotopes.\Question: Choose the right answer from options given a) nine b) eight c) three d) two
[EX A]:
d