Please help ASAP ! Which historical event BEST demonstrates the operation of checks and balances?

A) The Senate approved the appointment of Clarence Thomas to the Supreme Court.

B) South Carolina seceded from the Union over the issues of slavery and States rights.

C) President George Washington used the Army to suppress a tax rebellion by Pennsylvania farmers.

D) President Dwight D. Eisenhower sent Federal troops to enforce the integration of public schools in Little Rock, Arkansas.