They are showing two important works by Calder.

They are showing two important works by Calder.

~ Because it is the following work:

A piece for symphony orchestra, choir and four soloists.

A piece of music suitable for symphony orchestra, choir and quartet.

~ from is a passage from ...:

She read a passage from Alice in Wonderland.

She read a passage from Alice in Wonderland.

~ of a...：

A piece of jewelry

A piece of jewelry

Phrase [collocation]

A piece of music/sculpture/work/work

A piece of music; A sculpture; A work; An article