This museum (has, have) been called the best of all the Smithsonian museums.

• has

• have

This enormous building (covers, cover) three blocks.

• cover

• covers

Twenty-three galleries (offers, offer) visitors information and entertainment.

• offers

• offer

The different showrooms (deals, deal) with various aspects of air and space travel.

• deals

• deal

As you can see, the exhibits (features, feature) antique aircraft as well as modern spacecraft.

• features

• feature

In another area, a theater (shows, show) films on a five-story-high screen.

• shows

• show

A planetarium (is, are) located on the second floor.

• is

• are

Projectors (casts, cast) realistic images of stars on the ceiling.

• casts

• cast

Some tours (is, are) conducted by pilots.

• is

• are

 In addition, the museum (houses, house) a large research library.

• houses

• house