1. The girl who is playing in the garden is my younger sister.

→ ở đây ta dùng MĐQH "who" để thay thế cho từ "the girl" - tức là "she"

N(người) + who + V

2. Unless you drive carefully, you will cause accident.

→ If not = Unless 

3. My brother said (that) he would go to Vung Tau the following week/ the next week.

→ S + said (that) + S + V(lùi thì) ( ở câu này ta chuyển "will" → "would" - "next week" → " the following week/ the next week " )

4. Unless he studies hard, he won't pass the coming exam.

→ giải thích tương tự câu 2

1.The giro who is playing in the garden is my younger sister.

2.Unless you drive carefully,you will cause accident.

3.My bother said that she would go to Vung Tau the following week.

4.Unless he studies hard,he will pas the coming exam.