#MHT
1. It's very important to keep the environment clean.
V-ing -> to-V
Keeping -> To keep

2. I haven't spoken to her for 3 years.
QKĐ -> HTHT
CT HTHT: S + have/ has not + V3 + O.... 
Since -> For
Last spoke -> Haven't spoken

3. Tam used to type faster than now.
Used+ To-V: Đã từng làm
⇔ Có kinh nghiệm
⇔ Đánh nhanh hơn

4. It is Lan's fifteenth birthday next week.

5. When did you use a pen?
HTHT -> QKĐ
CT QKĐ: When + did + S + V-inf +O...?

Chúc bạn học tốt, xin hay nhất!