Công thức thì HTHT

(+) S + has/have + V3/ed 

(-) S + has/have + not + V3/ed 

(?) Has/Have + S+ V3/ed?

DHNB: before, since + mốc thời gian, for + khoảng thời gian, yet, already, just,....

Công thức thì QKĐ (V: thường)

(+) S + V2/ed 

(-) S + didn't + V1 

(?) Did + S+ V1?

DHNB: ago, last (year, month ...), yesterday, in + năm QK, …

--------------------------------------------------------------

1. have already seen

DHNB: already (HTHT)

2. has worked / started

DHNB: for sixteen years (HTHT) - ago (QKD)

3. Have you ever met / sat 

DHNB: ever (HTHT) - last summer (QKD)

4. did you start / have recently completed / asked 

DHNB: ago (QKD) / recently (HTHT)

`color{orange}{~STMIN~}`