I.

1. Ba has learnt English since 2013.

→ S + started + to_V/V_ing +in + time: bắt đầu làm gì

= S + have/has + V3/ed + since + time

2. I wish I knew many English words.

→ S + wish(es) + S + v2/ed: present wish

3. It is dangerous to swim in the river.

→ S + Vbe + Adj + to_V

4. This school was built 30 years ago.

→ câu bị động thì QKĐ: S + was/were + V3/ed + (by+O) + time

5. The teacher asked me how many students there were in my class.

→ S + asked + O + Wh/H + S + V(lùi thì): câu tường thuật dạng câu hỏi Wh/H ( lùi thì HTĐ → QKĐ )

II.

1. Would you mind turning off the fan?

→ Would you mind + V_ing: Bạn có phiền...

2. Nam is interested in playing basketball in the morning.

→ be interested in + V_ing = like + V_ing: thích làm gì đó

3. She isn't old enough to ride a motorbike.

→ S + vbe + Adj + enough + (for+O) + to_V - ở đây trai nghĩa với 'young' là 'old' nên ta dùng 'old'

4. Although the weather was bad, we went to the cinema together.

→ Although + S + V, S + V = Despite/In spite of + N/V_ing, S + V

5. You had better not eat too much meat.

→ should (not) + V0 = had better (not) + V0: (không) nên làm gì

1. Ba has learnt English since 2013.

-> S + started + to V/ Ving + in + mốc thời gian = S + have/has + Vpp + since + mốc thời gian

2. I wish I knew many English words.

-> Câu mong ước nên lùi thì, chuyển phủ định sang khẳng định.

3. It is dangerous to swim in the river.

-> It + be + adj + to V

4. This school was built 30 years ago. 

-> Câu bị động quá khứ đơn: S + was/were + Vpp

5. The teacher asked me how many students there were in my class.

-> Câu trần thuật nên lùi thì từ "are" thành "were" 

II

1. Would you mind turning off the fan ?

-> mind + Ving: Bạn có phiền khi làm gì đó 

2. Nam is interested in playing basketball in the morning.

-> be interested in + N/Ving: thích 

3. She isn't old enough to ride a motorbike.

-> S + be + adj + enough + to V

4. Although the weather was bad, we went to the cinema together.

-> Although + S + V: mặc dù

5. You had better not eat too much meat.

-> had better = should