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').

Example Input: Most school aged children pass at least ____ stools per week, with an average of one stool per day.\Question: Choose the right answer from options given a) three b) one c) six d) zero
Example Output: a

Example Input: Normal cells have ____ copies of each chromosome.\Question: Choose the right answer from options given a) two b) five c) eight d) no
Example Output: a

Example Input: Many magnetometers are ____ axis.\Question: Choose the right answer from options given a) four b) six c) zero d) three
Example Output:
d