I have to fill in the blank in the extract below.

Tom: Have you heard the news about David?

Harriet: No. (what/happen)?

I put in what has happened and I guess that's the only possibility. However, suppose the extract was

Tom: Have you heard the news about David? He has had an accident.

Harriet: Really? (what/happen)?

It seems to me that what happened should be used here. So what do you think? Note that the exceprt is from a British English grammar book.
Do the directions tell you to use the present perfect? If the directions for the exercise don't specifically say you should fill it in with the present perfect, then yes, either could be used.

What happened?

What has happened?

What's happened? (using a contraction for what has)

These would all be correct, but it depends on what the directions for the exercise tell you to do.

Chalk
motor_angelTom: Have you heard the news about David?
Harriet: No. (what/happen)?
I put in what has happened and I guess that's the only possibility.
No! The standard exchange is this:

- Have you heard the news ...? (Is this piece of information something you know already?)

- No. What happened? (No. Tell me the story about it.)

Likewise:

- I've just seen the latest Jim Carrey movie. Have you seen it?

- No. How was it? (You would never say How has it been!)

CJ
Teachers: We supply a list of EFL job vacancies
Tom:He (walk ) down some steps