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]: Chemical interactions are essentially electron interactions of ____ atoms.\Question: Choose the right answer from options given a) six b) no c) ten d) two
[EX A]: d

[EX Q]: Altimetric satellites are usually limited life missions lasting approximately three to ____ years.\Question: Choose the right answer from options given a) five b) ten c) four d) eight
[EX A]: b

[EX Q]: Most people develop antibodies within three months and some can take up to ____ months.\Question: Choose the right answer from options given a) zero b) eight c) six d) seven
[EX A]:
c