The correct answer is D) too many Slave states being added to the Union.
The biggest reason for compromises on the slave issue was "too many Slave states being added to the Union."
The Great Compromise of 1787, also known as the Connecticut Compromise was the opportunity for both, larger and smaller states to reach an agreement that solved their differences regarding the representation each state should have in under the Constitution. The agreement also defined the participation of the states in Congress. These negotiations allowed the formation of a Congress with two chambers of legislators.