Answer:
The good answer is:
c. Cloture can only be achieved by a three-fifths vote, and parties don't usually have that kind of majority.
Explanation:
Cloture is the only legal resource to overcome filibuster. Cloture is a limit on the time allowed for consideration of a bill. But to get it approved, 60 votes in the Senate, or three-fifths, are neccessary. No party usually enjoys the privilege of being able to gather such a majority.
