1. we began donating books and clothes since 2015. (trường hợp này dùng began{begin} + V_ing để diễn tả hành động là thói quen, được lặp đi lặp lại nha, mình nghĩ z hihi :))
2. I haven't painted a mural over graffiti for 5 months ago.
3. Because Minh was lazy, he failed the exam.
4. We should eat a lot of fruit and vegetables everday.
5. I'm leaving now so that I don't miss the train.   

=>
1. We began to donate books and clothes in 2015.
-> began to V : bắt đầu làm gì
2. I haven't painted a mural over graffiti for 5 months.
-> chuyển QKĐ sang HTHT,S have/has (not) V3/ed, for + khoảng thời gian
3. Because Minh was lazy, he failed the exam.
-> because S V : bởi vì
4. We should eat a lot of fruit and vegetables every day.
-> should V : nên làm gì
5. I'm leaving now so as not to miss the train./I'm leaving now so that I won't miss the train.
-> so as (not) to V : để (không) ~ so that S V