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 Input:
Natural chlorine contains ____ isotopes.\Question: Choose the right answer from options given a) two b) six c) eight d) seven

Ex Output:
a


Ex Input:
Carbon forms ____ bonds.\Question: Choose the right answer from options given a) five b) four c) two d) three

Ex Output:
b


Ex Input:
Smoking is responsible for ____ in five deaths in the United States.\Question: Choose the right answer from options given a) five b) eight c) one d) seven

Ex Output:

c