86. It is over three months since Peter last had his hair cut.
( It is [time] since sb did sth: đã bao lâu kể từ khi ai đó làm điều gì)
87. Only if you increase the publicity will people become aware of the problem.
(Đảo ngữ: Only if [clause] aux V [clause]: Chỉ khi... thì)
88. Enormous effort has been made to find a cure for AIDS.
(Các nhà khoa học đã rất cố gắng tìm ra cách chữa khỏi bệnh AIDS.=Những nỗ lực to lớn đã được làm ra để chữa khỏi bệnh AIDS)
89. The harder you work, the more successful you are.
(The comparative + clause , the comparative+ clause: Càng...càng...)
90. Were you to change your mind, you would be welcomed to join our class.
(Cấu trúc đảo câu điều kiện loại 2: Were S to V, S would V)