`11.` The last time I donated my blood was 7 months ago.

`->` The last time + S + V2/ed + was + time + ago

`=` S + last + V2/ed + time + ago

`12.` How long have you done charitable work?

`->` How long + have/has + S + V3/ed?

`=` When + did + S + start/begin + V-ing/to V?

`13.` She last involved in community service 2 months ago.

`->` The last time + S + V2/ed + was + time + ago

`=` S + last + V2/ed + time + ago

`14.` I have worked as an activist since I was 20 years old.

`->` S + have/has + Vpp + for/since + time

`=` S + started/began + V-ing + time + ago

`15.` It has been one year since my best friend gave up eating fast food.

`->` It + has been + time + since + S + gave up + V-ing

`=` S + gave up + V-ing + time (quá khứ)

`11`.The last time I donated my blood was `7` months ago

`->` The last time + S + Ved / V2 + was + time / timeline 

`=>` Lần cuối làm gì

`12`.How long have you done charitable work ?

`->` Thì HTHT ( NV ) : Have / Has + S + VpII ?

`=>` Have `+` You , They

`->` How long dùng để hỏi về bao lâu [ Tương đương với " for " ]

`13`.She last involved in community service `2` months ago

`->` S + last + Ved / V2 + time / timeline : Lần cuối làm gì

`14`.I have worked as an activist since I was `20` years old

`->` Thì HTHT : S + have / has + VpII

`=>` I , You , We , They `+` have

`->` Since + Timeline : Từ khi nào

`15`.It has been one year since my best friend last ate fast food

`->` It + is / has been + time / timeline + since + S + last + Ved / V2

`=>` Đã bao lâu kể từ khi lần cuối làm gì

`\text{# TF}`