The answer is actually C.
-C. They would change the balance in congress.
Step-by-step explanation:
The north wanted a slave free country, while the south did not. Once California became a part of the U.S as a free slave state, there were more free slave states in congress than non-free slave states. Now, the south thought that other states would be influnced in chossing to be a free slave state. So this would cause a great debate.