1. I buy these pencil-cases in this book store
=> These pencil-cases are bought in the book store
2.He send a letter to his parents every week
=> A letter is sent to his parents every week
Giải thích :
_ Bị động thì hiện tại đơn :
(+)S + Is/am/are + PII (by.......)
(-) S + is/am/are + not + PII (By.......)
(?) Is/Am/Are + S + PII (by......)?