15. He couldn't  be helped ( s+ could + be + vpll)

16. He asked me to do that test again ( S+ asked + O + (not) + to V)

17. He asked me where the post office was (S + asked+ WH + S +V…)

18. I will be invited to the party by Bill ( S + WILL BE + VPLL)

19. If i had the key, i could get into the house (If + S + V2/ Ved, S +would....+ V)

20.I used to getting up early in the morning. ( S+used to + V).

xinhaynhat

${15.}$ He couldn't be helped.

→ bị động dạng động từ khiếm khuyết: S + can/could/should/must/may ... (not) + be + v3/ed +(by+O) + time

${16.}$ He told me to do that test again.

→ told sb to do sth: bảo ai đó làm gì

${17.}$ He asked me where the post office was.

→ câu gián tiếp dạng câu hỏi wh/h: S + asked + O + wh/h + S + V(lùi thì) - ở đây ta lùi thì HTĐ → QKĐ

${18.}$ Bill should be invited to the party.

→ bị động dạng động từ khiếm khuyết

${19.}$ If I had the key, I could get into the house.

→ câu ĐK loại 2 ( diễn tả 1 sự việc không thể xảy ra ở hiện tại ): If + S + QKĐ, S + would/could (not) + V0

${20.}$ I used to get up early in the morning.

→ used to do sth: đã từng làm việc gì