S + had + V3 + O (for/since/before/after)
I had finished my homework before she called.
By the time I arrived, he had left.
2
Quan hệ thời gian
BEFORE: Hành động A xảy ra TRƯỚC hành động B
After she LEFT, I ARRIVED. (Leave → Past Perfect)
AFTER: Sau khi
AFTER: After he HAD EATEN, he went out.
3
Past Perfect vs Quá khứ đơn
Khi nói về 2 hành động quá khứ:
→ Hành động xảy ra TRƯỚC: Past Perfect
→ Hành động xảy ra SAU: Past Simple
When I GOT there (QKĐ), she had LEFT (QKHT - trước đó)