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.
The biggest reason for compromises on the slave issue was that too many slave states being added to the Union, which basically means that if they were to be admitted, as slave states, some other conditions would have to also be fulfilled in order to keep the congress equlibrium. Such example can be the separation of Maine and its addition to the Union as a non slave state in order to compensate the fact that Missouri would be added as a slave state
