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]: Tetrapods are animals that have ____ legs or leg-like appendages.\Question: Choose the right answer from options given a) four b) one c) ten d) six
[EX A]: a

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

[EX Q]: Red algae are haplo-diplonts with a complicated life cycle that often involves ____ phases.\Question: Choose the right answer from options given a) three b) no c) six d) seven
[EX A]:
a