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]: Female cats can go into heat for the first time as early as ____ months of age.\Question: Choose the right answer from options given a) four b) zero c) five d) eight
[EX A]: c

[EX Q]: Acoustic guitars come in ____ types.\Question: Choose the right answer from options given a) two b) ten c) one d) four
[EX A]: a

[EX Q]: English braille consists of ____ grades of braille.\Question: Choose the right answer from options given a) one b) ten c) eight d) three
[EX A]:
d