What are earthworks?
a. artistic pieces that involve materials from nature
b. artistic pieces that involve preserving an area in danger
c. artistic pieces that involve raw materials found at the site of the piece
d. natural artistic pieces formed without human influence

   C. Artistic pieces that involve raw materials found at the site of the piece

Explanation:  Given that artistic answers are offered, earthworks or earth art, land art are offered, is an artistic movement that appeared in America and Great Britain in the 60's and 70's of the 20th century but expanded to other countries. This artistic expression involves the use of natural materials that found on site. Those materials from which the artistic works of relief shape are made on the ground itself can be vegetation, wood, stones, soil, etc, and the location of works is usually in a natural environment far from the populated areas.

yes

explanation: