A: Excuse-me, do you understand about this?
B: Yes I do, I Understand about this
A: Ok, I'm just making sure that you understand about this.
B: It's ok, If I don't understand anything, I'll call for your help
A: Okay, see you then
A: do you understand what mrs. emma explained to us yasterday?
b: yes, of course. why?
a: nothing, I just want to ask you.
b: okay.