Northern attempts to attack slavery was limited by?

A) the apathy of most northerners regarding the question

B) the presence of more important issues before congress

C) the absence of strong northern congressional leadership

D) the amount of money slave industries contributed to the national economy

E) the absence of federal authority to regulate slavery

I don't believe that "A" is the answer because Northerners were not apathetic at all about slavery. I am unsure of the answer but I am leaning towards "E" E is the correct answer