Power generators are a significant source of three key  sulfur dioxide (SO2), nitrogen oxide (NOx), and mercury (Hg).
The power generators make a lot of sulfur dioxide.
The power generators are the only source for mercury.
Two children are playing in the park.
The Palais des Beaux Arts only has a small collection.
It's a desolate road in rural England.
It's impossible to start a guided tour before the official closing time.
I will never play racquetball again.
It is warm and windy.