1. An overcrowded school

One disadvantage of an overcrowded school is that students don’t have enough space to play. Healthcare is not good and air pollution could be bad.

2. An overcrowded bus 

One disadvantage of an overcrowded bus is that people don’t have enough seats to sit down. The bus will be so uncomfortable.

3. An overcrowded block of flats 

One disadvantage of an overcrowded block of flats is that the place will be noisy. The atmosphere is not fresh.

→ Advantages:
   - Have more friends
   - Have better quality because if the school has more students, the headteacher will update the quality of the school
→ Disadvantages:
   - Don't have enough seats
   - Some students can easily commit crime
   - Don't have enough freshwater to use
P/s: Mình mới nghĩ được như vậy thôi nha^^