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 aphthous ulcers heal in one to ____ weeks.\Question: Choose the right answer from options given a) two b) eight c) one d) seven
Example Output: a

Example Input: Ostriches usually live in groups, most commonly ____ male with three females.\Question: Choose the right answer from options given a) seven b) two c) one d) nine
Example Output:
c