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]: Tardigrades are microscopic, water-dwelling, segmented animals with ____ legs.\Question: Choose the right answer from options given a) eight b) nine c) one d) seven
[A]: a

[Q]: Ocular dryness responds to the use of artificial tears applied every ____ to three hours.\Question: Choose the right answer from options given a) no b) one c) three d) eight
[A]: b

[Q]: Water is visualized as occupying the center of a tetrahedron, a solid with ____ faces.\Question: Choose the right answer from options given a) four b) ten c) seven d) zero
[A]:
a