Practice!

Sample Problem

Not many trees grow in the tundra because

(A) it doesn’t receive enough rainfall

(B) the permafrost prevents proper water infiltration

(C) it is too cold

(D) the soil contains chemicals excreted by lichens that prevent tree growth

Solution

(A) and (B) are the correct answers. (C) isn’t true because there are trees in other biomes adapted to extremely cold conditions. And (D) isn’t true at all.