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').

Real airplanes have round engines and ____ wings.\Question: Choose the right answer from options given a) four b) six c) three d) two
d

Dunes are of ____ types - linear and parabolic.\Question: Choose the right answer from options given a) three b) four c) ten d) two
d

Newborn pandas cry for milk about every ____ hours.\Question: Choose the right answer from options given a) zero b) four c) three d) two
d