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]: Color codes are ____ digit combinations of letters and numbers that correspond to a specific color.\Question: Choose the right answer from options given a) six b) eight c) seven d) one
[A]: a

[Q]: Photosynthesis occurs in ____ phases.\Question: Choose the right answer from options given a) four b) two c) nine d) five
[A]: b

[Q]: Most scientists consider swamp s, marsh es, and bog s to be the ____ major kinds of wetlands.\Question: Choose the right answer from options given a) six b) five c) three d) seven
[A]:
c