They are collecting recyclable materials.

他们正在收集可回收材料。

同一单元的其他句子

• I'll help to clean up the city parks this weekend.这个周末我将帮助清理城市公园。
• We should pick up trash in the park after the picnic.野餐后我们应该在公园里捡垃圾。
• She is going to plant trees in the park next Sunday.她下周日将在公园里种树。
• Can you join us to clean up the river bank?你能加入我们清理河岸吗？
• Don't throw rubbish on the ground in public places.不要在公共场所的地上扔垃圾。