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 HTTD 

(+) S + am/is/are + Ving 

(-) S + am/is/are + not + Ving 

(?) Am/Is/Are +S +Ving? 

DHNB: now, right now, (!), at present, at the moment,.....

Công thức thì QKTD 

(+) S + was/were + Ving 

(-) S + was/were+ not + Ving 

(?) Was/Were +S +Ving? 

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. is working

DHNB: at the moment (HTTD)

2. have just received 

DHNB: just (HTHT)

3. saw / was waiting

QKD + when + QKTD

4. were you doing / phoned 

5. visited

DHNB: last summer holiday (QKD)

6. were talking / was reading

7. was learning

DHNB: at 7pm yesterday (QKTD)

8. has never watched 

DHNB: never (HTHT)

9. has read

DHNB: before (HTHT)

10. haven't seen / saw

DHNB: for a long time (HTHT) - ago (QKD)

`color{orange}{~LeAiFuRuiHuiBao~}`