1. Sue: What's going on, Joe?
Joe: Well, because the bus was late.
No. 'Because' is used to answer questions beginning with 'why ...?' (asking for a reason). But here Sue is not asking for the reason for something. She wants a description of the situation.
2. Sue: What's going on Joe?
Joe: We're in a hurry, because the bus was late.
Yes. This time Joe describes what he is doing (hurrying), and he gives the extra information that this is because the bus was late.
3. Tom: I'm not sure how to do this.
Harriet: It's easy. Look, you write here and sign here.
Yes. Tom's statement is an implicit request for Harriet to give an explanation. This means that though Tom does not make a direct (explicit) request for an explanation, Harriet can understand from what he has said that he needs her to explain.
4. Mother: Stop that! What are you doing?
Bill: Wait. I can explain. It's like this ..
Yes. Bill starts by saying 'wait' to tell his mother not to get upset. Then he begins by telling her that he is going to give her the explanation for what he is doing. He is also giving himself time to prepare the explanation in his own mind.
5. Jane: Why are we going already?
Mr Black: We have to meet Janet soon.
No. Jane knows that she has asked Mr Black for a reason, so she understands that there is a 'because' at the start of the sentence, even though Mr Black did not say it. (When you don't say something because you know the other person understands it is there, this is called ellipsis)
6. Harry: Can you tell me how to do this?
William: Finally, you do this and this, and it works, see?
No. William has explained correctly, but he has started with the word 'finally'. You should only use this for the very last part of the explanation.
7. Harry: Can you tell me if this is right?
William: Well, first of all, you need to change this ...
Yes. William has seen that there are several things he needs to explain, so he tells Harry to expect several parts in his explanation by beginning with 'first of all ..'.
8. Mike: I have to go to London on Saturday.
Tanya: Does this mean that I won't see you then?
Yes. Tanya thought that she might see Mike on Saturday. Now she thinks that she might not, because Mike is going to London, so she is asking him to explain the situation.
