[susan53]

You said : A: I have just done what had been asked me yesterday.
B: I have just done what was asked me yesterday.
C: I just did what had been asked me yesterday.

Which of these three sentences is correct?
Can I use the past simple (case b) to express an action which happened before another or I have to choose the Past Perfect?

All three questions are incorrect, but the verb forms in (B) are correct. It should be :

B: I have just done what was asked of me yesterday.

Even that's a bit strange - but I think your question is about the verb forms, so let's concentrate on those.

You'll find the explanations for the two verb form "have just done" and "was asked" above. One is seen as impacting upon the present (I've done it, so it's not a problem any more) while the second is firmly established in past time (yesterday) and therefore needs a past simple verb ( in this case past simple passive, but that makes no difference).

The past perfect is only used to sequence two past events - so A is impossible because it includes a present (perfect) event and a past event, not two past events.

It is optional (and often not used) if there is another indicator of the sequencing in the sentence - eg :
After the meeting finished, we went for a pizza.
After the meeting had finished , we went for a pizza.
Here, "after" indicates the sequence. The past perfect verb form is therefore unnecessary (though optional).

Similarly in sentence C, "just" indicates that this is the most recent event. So the past perfect is unnecessary as a sequencer.


The past perfect is only obligatory if, otherwise, the sequence would be unclear. Compare :
David left when we arrived. (= D. left as/just after we arrived)
David had left when we arrived. (= D. left before we arrived)