`=>` It's `4` months since I last went to school because of COVID-`19`

`-` Cấu trúc: It's + time + since + S + (last) + V-ed/V2 + O: Đã bao lâu kể từ lần cuối làm gì

`->` I last went to school `4` months ago because of COVID-`19` 

`-` Cấu trúc: S + last + V-ed/V2 + O + thời gian trong QK: Lần cuối làm gì là...

`->` The last time I went to school was `4` months ago because of COVID-`19`

`-` Cấu trúc: The last time + S + V-ed/V2 + O + was + time + ago: Lần cuối làm gì là bao lâu về trước...

`=` S + haven't/hasn't + VpII + O + for + khoảng thời gian/since + mốc thời gian: Đã không làm gì được bao lâu ..

`\color{green}{#Queen}`

`=>` It is 4 months since I (last) went to school because of COVID-19.

`-` $\text{It is + time + since + S + (last) + V-ed}$ 

`=>` I last went to school 4 months ago because of COVID-19.

`-` $\text{S + last + V-ed + time + ago}$ 

`=>` The last time I went to school was 4 months ago because of COVID-19.

`-` $\text{The last time + S + V-ed + was + time + ago}$