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: All spider mites have ____ legs and a lack of a separate head.\Question: Choose the right answer from options given a) eight b) four c) ten d) one

A: a
****
Q: Reverse osmosis uses ____ to ten gallons of water to produce one gallon of drinking water.\Question: Choose the right answer from options given a) two b) zero c) five d) three

A: d
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Q: Presidential elections occur once every ____ years.\Question: Choose the right answer from options given a) nine b) five c) four d) eight

A:
c
****