The words "high altitudes, harsh climate, and few trees" describes A. Alpine ecosystems in the United States. B is incorrect because Deciduous forest ecosystems have many trees. While C and D can have harsh climates and few trees, deserts and grasslands in the US are at very low altitudes. A is the only correct answer because alpine (mountainous) regions are very high thereby resulting in harsh climates that do not allow for the growth of many trees.
