Question

They collect pebbles into passive voice​

Answer 1

Answer:

pebbles are collected by them

I think this to be the answer

but I have some doubt

Answer 2

Answer:

Explanation:

Degradable or non - persistent pollutants: The pollutants that can be rapidly decomposed by natural processes is called degradable or non-persistent pollutants. E.g.- sewage, paper products, vegetables, juice, seeds and leaves. They are only harmful when present in large quantities within the environment.