What was the main effect of the contract with america? a. the constitution was amended. b. democrats lost the white house. c. the senate impeached bill clinton. d. republicans took control of congress.

The correct option is D.
Contract with America was a ten points reform plan, which Republican 1994 USA election candidates promised to put in place if they are voted in and gained the control of the congress. Due to this reform plan, the masses voted massively for the Republican candidates and the Republican won and were giving control of both the houses of congress. 

This resulted for the Republicans to win that is why they take control on the congress. The main effect of the Contract With America is that D.Republicans took control of Congress. This was a deal in which people voted more on the republicans at that time.