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]: Color codes are ____ digit combinations of letters and numbers that correspond to a specific color.\Question: Choose the right answer from options given a) six b) eight c) seven d) one
[EX A]: a

[EX Q]: Coffee trees reach maturity between ____ and four years when their clusters of fruit turn deep red.\Question: Choose the right answer from options given a) no b) three c) nine d) five
[EX A]: b

[EX Q]: National immunisation vaccinates all children under ____ against polio.\Question: Choose the right answer from options given a) three b) five c) one d) four
[EX A]:
d