Rearrange the parts to make a meaningful sentence.

P. throw plastic bags into

Q. please do not

R. the river because they

S. harm the fish

Explanation

1. 01

   Q begins a request, and "do not" needs a verb: P "throw plastic bags into".

2. 02

   "Into" needs a place: R "the river", then "because they" begins the reason. S gives its verb.

3. 03

   So the order is QPRS: "Please do not throw plastic bags into the river because they harm the fish."