${15.}$ Is the test done well by Mai?

→ bị động HTĐ: S + is/am/are (not) + V3/ed +(by+O) + time 

${16.}$ The gate has never been repainted gray by our father.

→ bị động HTHT: S + have/has (not) + been + V3/ed +(by+O) + time 

${17.}$ A song wasn't being sung by Alex when the doorbell rang.

→ bị động QKTD: S + was/were (not) + being + V3/ed +(by+O) + time 

${18.}$ The floor mustn't be cleaned by the students every day.

→ bị động động từ khuyết thiếu: S + can/could/should/may/might/must ... (not) + be + V3/ed +(by+O) + time 

${19.}$ The dog is usually fed by my mother.

→ bị động HTĐ

${20.}$ The train can't be used by a lot of people.

→ bị động động từ khuyết thiếu: S + can/could/should/may/might/must ... (not) + be + V3/ed +(by+O) + time 

${21.}$ The eggs have been eaten by the little girl.

→ bị động HTHT

${22.}$ Soccer is played all over the world.

→ bị động HTĐ

Đáp án:

`15.` Is the test done well by Mai?

`16.` The gate has never been repainted gray by our father.

`17.` A song wasn't being sung by Alex when the doorbell rang.

`18.` The floor mustn't be cleaned by the students every day.

`19.` The dog is usually fed by my mother.

`20.` The train can't be used by a lot of people.

`21.` The eggs have been eaten by the little girl.

`22.` Soccer is played all over the world.

`-` Cấu trúc câu bị động:

`+` Thì HTĐ: S + am/is/are (not) + PII + (by  o)...

`+` Thì QKĐ: S + was/were (not) + PII + (by  o)...

`+` Thì HTHT: S + have/has (not) + PII + (by o)...

`+` Thì HTTD: S + am/is/are (not) + being + PII + (by  o)...

`+` với từ must(not): S + must (not) + be + PII + (by   o)...

`+` với từ can(not): S + can (not) + be + PII + (by   o)...