$\text{Đáp án :}$
`1` . The girl who lived next door to us is very friendly.
`->` Who thay cho "the girl" dùng để chỉ người
`2` . Because it rained heavily , they were late for school.
`->` Because + S + V : bởi vì `-` chỉ nguyên nhân
`3` . I enjoy reading book in my free time.
`->` enjoy doing sth = interested in doing sth : thích làm gì
`4` . Hellen should prepare her homework more carefully .
`->` Should do sth : nên làm gì
`Chan`
