Mike: Hey, Liam, I need your advice. I'm having trouble with my math homework.
Liam: Sure, what's up? I'm pretty good at math.
Mike: Well, I don't understand how to solve this equation. Can you explain it to me?
Liam: Of course. First, you need to isolate the variable, because that's the easiest way to start.
Which sentence from the dialogue is an explanation or gives a reason?
A) I need your advice.
B) I'm pretty good at math.
C) Can you explain it to me?
D) First, you need to isolate the variable, because that's the easiest way to start.