Right, you need to know certain things. But the point of the question is not that you know what a B-tree is a have memorized a fact about the btree. The point is the followup question, which requires you to understand the consequences of using different kinds of trees. That's not the sort of thing you memorize, it's the sort of thing you internalize. If you can't answer the second question, you probably wouldn't know enough about trees to be able to casually think about certain problems you might come across in "systems programming".