`9.` Their friend is often given a card (by them) on their friend’s birthday.

      A card is often given to their friend (by them) on their friend’s birthday.

`-` Câu có hai tân ngữ.

`-` give - gave - given: cho

`10.` The east is risen by the sun.

`-` rise - rose - risen: mọc

`11.` The telephone was invented by Graham Bell many years ago.

`-` DHNB`:` ago `=>` Thì quá khứ đ ơn

`12.` A strange man was seen in my garden (by me) yesterday.

`-` see - saw - seen: nhìn, thấy

`13.` The problem was solved easily.

`14.` These cars were made in the USA (by them).

`-` make - made - made: làm

`15.` Many trees were planted in the school garden (by us).

`16.` I wasn't helped with my homework (by him).

`17.` Some comic books were bought for Lan's brother (by her).

`-` buy - bought - bought: mua

`18.` A letter was received by my sister yesterday.

`19.` I was sent this letter by Mary two days ago.

`-` send - sent - sent: gửi

`20.` I was asked a difficult questions by my teacher and I couldn’t answer.

_______________________

Bị động:

`-` Thì hiện tại đơn:
$(+)$ S + am/ is/ are + V(pp) + (by O).

$(-)$ S + am/ is/ are + not + V(pp) + (by O).

$(?)$ Am/ Is/ Are + S + V(pp) + (by O)?

`-` Thì quá khứ đơn:

$(+)$ S + was/ were + V(pp) + (by O).

$(-)$ S + was/ were + not + V(pp) + (by O).

$(?)$ Was/ Were + S + V(pp) + (by O)?

`-` by O đứng trước trạng từ chỉ thời gian, sau trạng từ chỉ nơi chốn.