Though Never Explicitly Intended, Which of the Following Has Been

Though never explicitly intended, which of the following has been a positive benefit of the competition for power between the two major parties?

A) Competition has been successful in keeping the government weak and under control.
B) The struggles between the two parties have kept third parties from confusing the goals of democracy.
C) Competition has proven to be a significant check against tyranny.
D) The two parties have been able to retain control of the government in the proper hands.
E) Most observers doubt that there are any positive benefits from political parties.