填空题
It is an ______ which may be brown, green or black in colour.
填空题
It gives us power for ______.
填空题
Petroleum that comes directly from deep in the ground is called ______.
填空题
At a refinery the crude oil is ______ into its various parts.
填空题
From the refined oil we obtain important products, such as gasoline, ______ , detergents,______, ______ , and perfumes.