Past Perfect - Quá khứ Hoàn thànhFORM of Past Perfect
The Past Perfect has two parts: the past tense of the verb 'to have' (=had) + the past
participle (PP) of the main verb. See examples below.
S + had + PP
I had learnt English.
He had swum well.
They had watched TV.
S + had not+ PP
I hadn't learnt English.
He hadn't swum well.
They had not watched TV.
Had + S + PP?
Had you learnt English?
Had he swum well?
Had they watched TV?

The Past Perfect refers to an event earlier than a specific event in the past. It is
used to make it clear that one event happened before another in the past. It does
not matter which event is mentioned first - the tense makes it clear which one
happened first.
In the following example, Event A happens before Event B.

You had studied English before you moved to New York

Even A Event B
When she got to the station,

the train has left