What would be the effect of high interest rates on credit cards? a) there would be no effect. b) more people would use credit cards. c) more people would use a debit card. d) fewer people would use credit cards.

C and D are likely correct.

High interest rates would likely dissuade people from using credit cards and would likely move them back to using their debit cards for purchases and to keep credit card purchases to ones that they knew they could pay back. You would end up getting people who were more desperate for the line of credit using it.