`@` `Answers & Solution`
1. You/volunteer/last summer.
2. How many/volutary activities/you/join/2020.
3. I/join/fun run/raise funds/a few days/ago.
`⇒`
1. You volunteered last summer.
`-` Dấu hiệu nhận biết Thì QKĐ: last summer
`@` Cấu trúc Thì QKĐ
( + ) S + V2/ed
( − ) S + didn't + V
( ? ) Wh_question + did + S + V?
2. How many voluntary activities did you join in 2020 ?
`-` How many + N đếm được số nhiều? 
3. I joined a fun run to raise funds a few days ago.
`@` Cấu trúc Thì QKĐ
( + ) S + V2/ed
( − ) S + didn't + V
( ? ) Wh_question + did + S + V?

$#ILNELY$

`1.` You volunteered last summer.

`2.` How many voluntary activities did you join in `2020`?

`-` How many + N đếm được số nhiều? 

`3.` I joined a fun run to raise funds a few days ago.

`-` A/an + adj + N

`@` QKD:

`(+)` S + V2/ed

`(-)` S + didn't + V

`(?)` (Wh_question) + did + S + V?