1. When we …(see) … them last night, they …(sing)… ; they …(say)… they …(sing)… since six o’clock.
-> saw/ were singing/ said/ had sung
2. We …(wait)… for you when you …(get)… back tomorrow.
-> will wait/ get
3. They …(not come)… home until they …(see)… everything.
-> won't come/ see
4. What do you think the children …(do)… when we get home ?
-> will be doing
5. I’m sure the letter won’t arrive in time unless it …(send)… by air
-> is sent

1. When we …saw … them last night, they …were singing… ; they …said… they …had been singing … since six o’clock.
2. We …will be waiting… for you when you …get… back tomorrow.
3. They …won't come)… home until they …see… everything.
4. What do you think the children …will be doing… when we get home ?
5. I’m sure the letter won’t arrive in time unless it …is sent… by air

Mốc đúng câu 2 còn lại sai hết nhé
câu 1. hành động kể lại xảy ra trong quá khứ, không có hiện tại hoàn thành ở đây đâu
câu 3. mệnh đề until will until v hiện tại
câu 4. mệnh đề when xảy ra trong 1 khoảng tgian
câu 5 câu bị động kết hợp câu đkien

1. saw/ were singing/ said/ had sung
2. will wait/ get
3. won't come/ see
4. will be doing
5. I’m sure the letter won’t arrive in time unless it …is sent… by air