单选题

Read the first sentence of a summary of the passage. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
The grasslands of North America consist mainly of the prairies in the Great Plains.
·______
·______
·______

A. Grasslands are found in the intermediate zone between dry desert and moist forest habitats.
B. Most of the native prairie grasses have been replaced with cereal crops and grasses for grazing.
C. Millions of glacial potholes that function as seasonal wetlands are an important feature of the region.
D. Waterfowl such as northern pintails, mallards, coots, and pied-billed grebes live in the northern Great Plains.
E. The prairie potholes have environmental value as a breeding ground for birds and as a potential carbon sink.

F. Storing 400 million tons of carbon is the equivalent of removing 4 million cars from the road.