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: Gases are perhaps the best understood of the ____ states of matter.\Question: Choose the right answer from options given a) three b) five c) nine d) zero

SOLUTION: a

PROBLEM: Astronomical observations suggest ____ or close to zero space-time curvature.\Question: Choose the right answer from options given a) six b) zero c) ten d) seven

SOLUTION: b

PROBLEM: Opossums are sexually mature at six to ____ months.\Question: Choose the right answer from options given a) seven b) two c) four d) eight

SOLUTION:
d