18. He hasn't been in touch with me for three weeks.
`=>` S + last + V2/ed + thời gian + ago = S + has/have + not + Vpp + for + thời gian
19. I haven't enjoyed myself since your birthday party.
`=>` S + has/have + not + Vpp + since + mốc thời gian
20. After she had washed the dishes, she watched TV
= Before she watched TV, she had washed the dishes.
`=>` After + quá khứ hoàn thành, quá khứ đơn = Before + quá khứ đơn, quá khứ hoàn thành
21. Before he left the office, he had called his wife.
`=>` Before + quá khứ đơn, quá khứ hoàn thành
22. After they had taken the pictures of the food, they enjoyed it.
23. While we were in the middle of our lesson, the teacher went out.
`=>` while: trong khoảng thời gian