plsssssssssssssssssssssssssssssssssssssssssssssssss

`1.` Have scientists discovered

`2.` haven't found

`3.` had taken `-` got

`->` After + S + had + P2, S + Ved/V2

`4.` has built `-` started

`->` HTHT `+` since `+` QKĐ

`(+)` S + Ved/V2

`5.` have bought

`6.` has spread

`----------`

$\text{*Structure: Present Perfect}$ (thì Hiện tại hoàn thành)

$\text{(+) S + have/has + P2}$

$\text{(-) S + have/has not + P2}$

$\text{(?) Have/Has + S + P2?}$

`DHNB:` since, for `+` khoảng thời gian,...