4) I’m studying computers because I want a good job.

Yes/No question:

Are you studying computers because you want a good job?

Yes, I am.

Question about the subject of the verb:

Who is studying computers because they want a good job?

I am.

Question about the action:

What are you doing?

I’m studying computers.

Other questions:

What are you studying?

Computers.

Why are you studying computers?

Because I want a good job.