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]: Diarrheal disease kills ____ million children every year.\Question: Choose the right answer from options given a) three b) no c) four d) ten
[A]: a


[Q]: Sexual reproduction involves ____ parents, one male and one female.\Question: Choose the right answer from options given a) zero b) two c) nine d) four
[A]: b


[Q]: Electrics usually have ____ strings.\Question: Choose the right answer from options given a) two b) eight c) four d) five
[A]:
d