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]: Natural tellurium consists of ____ isotopes.\Question: Choose the right answer from options given a) six b) seven c) eight d) one
[EX A]: c

[EX Q]: Manatees swim two to ____ miles per hour.\Question: Choose the right answer from options given a) no b) six c) five d) zero
[EX A]: b

[EX Q]: Lake Superior is the least polluted of the ____ lakes.\Question: Choose the right answer from options given a) three b) five c) four d) two
[EX A]:
b