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').

[Q]: Elephants give birth to one calf every ____ to nine years on average.\Question: Choose the right answer from options given a) no b) four c) three d) seven
[A]: b


[Q]: Most marine sediments are of ____ basic types.\Question: Choose the right answer from options given a) three b) ten c) two d) nine
[A]: c


[Q]: Diabetics are ____ to seven times more at risk for heart attack.\Question: Choose the right answer from options given a) five b) seven c) three d) zero
[A]:
c