`16.` Before Mike went to bed, he had turned off the light.

`->` Before + S + Ved/V2, S + had + P2

`17.` 

`-` I last visited the museum three months ago.

`-` The last time I visited the museum was three months ago.

`-` It's three months since I last visited the museum.

`->` S + last + Ved/V2 + time + ago

`=` S + have/has not + P2 + for + time

`=` The last time + S + Ved/V2 + was + time + ago

`=` It's + time + since + S + last + Ved/V2

`18.` John has played the piano for `10` years.

`->` S + began + V-ing + time + ago

`=` S + have/has + P2 + for + time

`16` After Mike had turned off the light , he went to bed .

`-` After + S + had + V3/V_ed + O , S + V(quá khứ) + O : Sau khi ai đó đã làm gì , ai đó mới làm gì ...

`17`

`@` The last time I visited the museum was three months ago .

`@` I last visited the museum three months ago .

`@` It was three months since I lats visted the museum .

`<=>` It + be + time + since + S + last + V(quá khứ) + O : Đã là bao lâu kể từ khi ai đó lần cuối làm gì ...

`<=>` S + have/has + not + V3/V_ed + O + time : Ai đó đã không làm gì trong bao lâu ...

`<=>` The last time + S + V(quá khứ) + O + was + time : Lần cuối ai đó làm gì là khi nào ...

`<=>` S + last + V(quá khứ) + O + time : Ai đó lần cuối làm gì khi nào ...

`18` John has played the piano for `10` years .

`-` S + have/has + V3/V_ed + O + time : Ai đó đã làm gì được bao lâu ...