The building technician ______ a gas leak in the offices on the fifth floor.

 

1. detected

2. detect

여기서 왜 detect 가 아니고 과거형인 detected가 되는건가요??

 

please make sure that the packages ______ sent to the trade fair in Berlin are ready by Friday

 

1. to be

2. was

3. are

4. have been

 

이 문장은 1번이 답인데 문장 구조도 이해가 안되고 왜 1번인지도 모르겠네요 ㅠㅠ