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').

Most children experience at least one episode by the time they are ____ years old.\Question: Choose the right answer from options given a) eight b) one c) ten d) seven
d

Voles are prolific breeders and can produce four to ____ litters a year.\Question: Choose the right answer from options given a) four b) two c) six d) three
c

Feline vision is about ____ times less acute than that of humans.\Question: Choose the right answer from options given a) ten b) five c) no d) two

a