sentences: humans discarding waste in an environment causes harm to that environment & discarding is similar to throwing & garbage means waste ->  humans throwing garbage in an environment causes harm to that environment  a body of water is a kind of environment & a stream is a kind of moving body of water ->  a stream is a kind of environment  humans throwing garbage in an environment causes harm to that environment & a stream is a kind of environment -> humans throwing garbage into a stream causes harm to the stream