(a) Harboring (hiding) fugitives
(b) Using violence to resist
(c) Running advertisements in the newspapers
(d) Refusing to cooperate with slave catchers
The correct answer is (c) Running advertisements in the newspapers.
Northerners used various methods to resist the capture of fugitive slaves, including harboring (hiding) fugitives, using violence to resist, and refusing to cooperate with slave catchers. They did not typically use advertisements in the newspapers as a means of resistance, as this could potentially draw attention to the fugitives and increase the risk of their capture.