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]: Nightmares happen frequently in childhood, especially between the ages of ____ and six.\Question: Choose the right answer from options given a) three b) eight c) no d) ten
[EX A]: a

[EX Q]: Human females have ____ X chromosomes.\Question: Choose the right answer from options given a) two b) six c) one d) eight
[EX A]: a

[EX Q]: Chemistry has ____ less important names.\Question: Choose the right answer from options given a) ten b) no c) eight d) nine
[EX A]:
b