Chọn một từ đúng trong ngoặc để hoàn thành mỗi câu sau

Chọn một từ đúng trong ngoặc để hoàn thành mỗi câu sau.

1. We love __ school because of its ancient beauty.                  (our/us)

2. He has worked as a singer ... 5 years.                                   (since/for)           

3.I can cook __ than my sister.                                                 (better/best)

4. Nam had a serious accident because he didn't drive _______.        (careful/carefully)