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:
Potassium helps maintain fluid regulation and normal pH. All ____ help normalize.\Question: Choose the right answer from options given a) three b) six c) two d) one

Ex Output:
a


Ex Input:
Ascidian tunicates come in ____ main forms.\Question: Choose the right answer from options given a) three b) zero c) four d) eight

Ex Output:
a


Ex Input:
Hair transplantation is an office procedure that takes approximately three to ____ hours.\Question: Choose the right answer from options given a) three b) four c) six d) no

Ex Output:

c