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: Vampires generally are male, and rabies is ____ times more frequent in men than in women.\Question: Choose the right answer from options given a) no b) two c) zero d) seven
Example Output: d

Example Input: Streptomyces are of special interest for ____ reasons.\Question: Choose the right answer from options given a) nine b) seven c) four d) two
Example Output: d

Example Input: Biological islands are of ____ general types, geographical and ecological.\Question: Choose the right answer from options given a) two b) six c) four d) one
Example Output:
a