Question

insert one comma to separate the coordinate adjectives.
designed by thom mayne and associates, the perot museum of nature and science is an exceptional award - winning structure. the building features an escalator housed in an unusual glass tube.

Explanation:

Coordinate adjectives are adjectives that can be reversed in order or separated by "and" without changing the meaning. Here, "exceptional" and "award - winning" are coordinate adjectives describing "structure", so a comma should be placed between them.

Answer:

Designed by Thom Mayne and associates, the Perot Museum of Nature and Science is an exceptional, award - winning structure. The building features an escalator housed in an unusual glass tube.