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

Example 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
Example Output: a

Example Input: Cleavage is perfect in ____ directions forming splintery fragments.\Question: Choose the right answer from options given a) two b) six c) no d) one
Example Output:
a