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').

[EX Q]: Pandas reach adulthood at about ____ years of age.\Question: Choose the right answer from options given a) eight b) seven c) five d) six
[EX A]: c

[EX Q]: Natural chlorine contains ____ isotopes.\Question: Choose the right answer from options given a) two b) six c) eight d) seven
[EX A]: a

[EX Q]: Many satellites orbit each of the ____ giant planets.\Question: Choose the right answer from options given a) eight b) four c) five d) six
[EX A]:
b