1. My father worked for the telephone company 20 years ago ( quá khứ đơn )
2. This test must be done carefully by all of the students
3. When I came to see Mr.Robinson last night, he was reading a newspaper ( quá khứ đơn )
4. John and Mary haven't contacted each other for a long time ( thì hiện tại hoàn thành )
5. If Hoa knows the answer, she would tell us immediately ( If + S + Verb (thì hiện tại), S + will (can, may) + Verb (nguyên mẫu) )