18. It wasn't Tom in the mall yesterday because he was in the hospital. I'm sure.

A. Tom needn't have been in the mall yesterday because he was in the hospital.

B. Tom should not have been in the mall yesterday because he was in the hospital.

C. Tom can not have been in the mall yesterday because he was in the hospital.

D. Tom must have been in the mall yesterday because he wasn't in the hospital.

=> Giải thích: Đây là động từ khuyết thiếu ở dạng Quá khứ

-> can't have(v-ed/vP3) : đáng lẽ không thể là ......

Tạm dịch : Tom đáng lẽ không thể ở trong trong trung tâm thương mại ngày hôm qua bởi vì anh ấy đã ở bệnh viện

Vậy chọn C