`1`. They will visit Da Lat tomorrow. 

`-` tomorrow: dấu hiệu thì TLĐ

`-` Câu khẳng định ( thì TLĐ): S+ will/ shall+ V

`2`. They are visiting Da Lat now.

`-` now: dấu hiệu thì HTTD

`-` Câu khẳng định ( thì HTTD): S+ is/ am/ are+ Ving

`3`. They visited Da Lat last summer.

`-` last summer: dấu hiệu thì QKĐ

`-` Câu khẳng định ( thì QKĐ): S+ Ved/ V2

`4`. They have visited Da Lat recently.

`-` recently: dấu hiệu thì HTHT

`-` Câu khẳng định ( thì HTHT): S+ have/ has+ Vpp

`5`. They visit Da Lat every summer.

`-` every summer: dấu hiệu thì HTĐ

`-` Câu khẳng định ( thì HTĐ): S( số nhiều)+ Vo

`6`. They will be visiting Da Lat at this time next summer.

`-` at this time next summer: dấu hiệu thì TLTD

`-` Câu khẳng định ( thì TLTD): S+ will/ shall+ be+ Ving

`7`. They were visiting at this time last year.

`-` at this time last year: dấu hiệu thì QKTD

`-` Câu khẳng định ( thì QKTD): S+ was/ were+ Ving

`-` Thì :

`+` HTĐ : S + Vs / es

`=>` `DHNB` : every , always , often , ...

`+` QKĐ : S + Ved / V2

`=>` `DHNB` : ago , last , yesterday , ...

`+` TLĐ : S + will + V

`=>` `DHNB` : tomorrow , in the future , next , ...

`+` HTTD : S + is / am / are + V-ing

`=>` `DHNB` : now , at the moment , at present , ...

`+` QKTD : S + was / were + V-ing

`=>` `DHNB` : at this time yesterday , this time yesterday , ...

`+` TLTD : S + will be + V-ing

`=>` `DHNB` : this time tomorrow , at this time tomorrow , ...

`+` HTHT : S + have / has + VpII

`=>` `DHNB` : recently , since , for , ...

`1`.They will visit Da Lat

`2`.They are visiting Da Lat

`3`.They visited Da Lat

`4`.They have visited Da Lat recently

`5`.They visit Da Lat every summer

`6`.They will be visiting at this time next summer

`7`.They were visiting at this time last year

`\text{# TF}`