14. They used to start these machines by hand

S + used to + v-inf (động từ nguyên mẫu)

15. These postcards were sent by our friends

S + was/ were + V3 (+ by Sb/ O)

16. This train ticket was ordered by Tim for his mother

S + was/ were + V3 (+ by Sb/ O)

`14`.They used to start these machines by hand

`\rightarrow` `\text{S + used to + V :}` Đã từng

`15`.These postcards are sent to us by our friends

`\rightarrow` Câu bị động - Thì HTĐ : `\text{S + be + V3 / PII ( by O )}`

`16`.This train ticket was ordered for his mother by Tim

`\rightarrow` Câu bị động - Thì QKĐ : `\text{S + was / were + V3 / PII ( by O )}`

`\text{@ TheFox}`