TASK DEFINITION: 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').
PROBLEM: Songbirds have ____ sets of vocal chords.\Question: Choose the right answer from options given a) six b) two c) eight d) ten

SOLUTION: b

PROBLEM: 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

SOLUTION: b

PROBLEM: Protons have ____ ups and a down.\Question: Choose the right answer from options given a) seven b) nine c) five d) two

SOLUTION:
d