`16.` haven't seen

Giải thích: since `->` thì HTHT

$\text{(-) S + have/has not + Ved/V3 + ...}$

`17.` have you known

Giải thích: thì HTHT

$\text{(?) Have/Has + S + Ved/V3 + ...?}$

`18.` were crossing `-` shouted

Giải thích: While `->` thì QKTD `|` sau phẩy là thì QKĐ

$\text{(+) S + was/were + V-ing + ...}$

$\text{(+) S + Ved/V2 + ...}$

`19.` were you doing

Giải thích: at this time yesterday `->` thì QKTD

$\text{(?) Was/Were + S + V-ing + ...?}$

`20.` won't rain `-` start

Giải thích: tomorrow `->` thì TLĐ `|` sau when là thì HTĐ

$\text{(-) S + will not + V-bare + ...}$

$\text{(+) S + V-(s/es) + ...}$

`21.` has played `-` was

Giải thích: since `->` thì HTHT `|` sau since là thì QKĐ với be

$\text{(+) S + have/has + Ved/V3 + ...}$

$\text{(+) S + was/were + ...}$

`22.` will never forget `-` have just told 

Giải thích: thì TLĐ `-` just `->` thì HTHT

$\text{(+) S + will + V-bare + ...}$

$\text{(+) S + have/has + Ved/V3}$

`23.` left `-` haven't heard.

Giải thích: ago `->` thì QKĐ `|` since `->` thì HTHT

$\text{(+) S + Ved/V2 + ...}$

$\text{(+) S + have/has + Ved/V3}$

`24.` won

Giải thích: in `2004` `->` thì QKĐ

$\text{(+) S + Ved/V2 + ...}$

`25.` were playing `-` was writting

Giải thích: while `->` thì QKTD

$\text{(+) S + was/were + V-ing + ...}$

$chucbanhoctot$
$\textit{~KaitoKid!}$