The grasslands of the midwestern United States have been grazed and farmed so that almost no grasslands remain with their original species of
plants and animals. How could people in the Midwest determine what kind of
natural ecosystem they are in?

A. Look in history books to determine what types of organisms lived
there before

B. Look around, since even a changed ecosystem is still an
ecosystem

C. Check yearly average rainfall

D. Check yearly average temperatures and see what types of plants
and animals live in those temperatures

B. Look around, since even a changed ecosystem is still an  ecosystem.

Explanation:

Ecosystem refers to the interaction or relationship that exist between living organisms and its surrounding environment. This environment provides habitat, food and other needs to the organisms. If the people in the Midwest determine what kind of  natural ecosystem they are in, they have to look around the environment they are living. This environment includes all the plants and animals that survive the change which occurs due to humans intervention.