The difference between list price & selling price is A) sales discount B) Trade discount C) purchase discount D) All E) None

The difference between the list price  and  the selling price is known as trade discount. So choice B is the answer for this question.

E) None.

I think this difference does not fall in any one discount category because List price is the value you are determining for your product at initial stage. It includes all types of discounts which may be offered when product goes in market. List price can vary from market and it can also change before sale.