1. We had just ( finish) finished dinner when they ( come) had come.
2. He had seldom (travel) traveled by bicycle before he (go) had gone to VietNam.
Giải thích: Past Perfect (thì quá khứ hoàn thành)
`(+)` `S+had+`$V_{3}$/`V`_`ed``+...`
`(-)` `S+hadn't+`$V_{3}$/`V`_`ed``+...`
`(?)` `Had+S+``$V_{3}$`/`V`_`ed``+...`