Thanks! I didn't know that one.
I had a teacher who became angry when a question was asked about a subject he felt students should already be knowledgeable about. "YOU ARE IN xTH GRADE AND STILL DON'T KNOW THIS?!" (intentional shouting uppercase). The fact that you learned it yesterday doesn't mean all humans in the world also learned it yesterday. Ask questions, always. Explain, always.
Such questions can be jarring though. I remember my "Unix Systems Programming" class in college. It's a third year course. The instructor was describing the layout of a process in memory, "here's the text segment, the data segment, etc." when a student asked, "Where do the comments go?"
:) true. I'm a teacher myself. I never dismiss questions, but I do get discouraged sometimes.