Question

read the excerpt from the text.
(2) tallgrass prairies are an extremely complicated web of life. at first sight, one sees a landscape dominated by grasses. eighty percent of the foliage is indeed made up of grasses, from 40 to 60 different species. the other 20% of the primary vegetation is made up of over 300 species of forbs or flowers. the prairie also has over 100 species of lichens and liverworts as well as numerous species of woody trees and shrubs along creeks and protected areas.
what is the central idea of this excerpt?
the central idea of this excerpt is that prairies
options:
contain a large diversity of plant life.
are mostly made up of grasses.
contain more flowers than lichens.
are complex and should be protected.

Explanation:

The excerpt describes tallgrass prairies, stating they have 40 - 60 grass species, over 300 forb/flower species, over 100 lichen and liverwort species, and numerous woody trees/shrubs. This shows a wide variety of plant life. The option "are mostly made up of grasses" focuses only on grasses (a part of the data), "contain more flowers than lichens" compares two subsets (not the main idea), and "are complex and should be protected" introduces a protection idea not in the excerpt. So the central idea is about diverse plant life.

Answer:

contain a large diversity of plant life.