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: Human malaria is caused by ____ species of Plasmodium . .\Question: Choose the right answer from options given a) six b) ten c) seven d) four
Example Output: d

Example Input: Most bioluminescence is blue for ____ reasons.\Question: Choose the right answer from options given a) seven b) two c) four d) zero
Example Output: b

Example Input: Life flows past the ____ dimensions of the body like radio waves escaping from an electrical wire.\Question: Choose the right answer from options given a) three b) seven c) four d) ten
Example Output:
a