"Surprising" Phenomenon
In forests that get a lot of acid rain, why are sugar maples more likely to show signs of decline consistent with calcium deficiency than are spruces or firs, even though all three kind of trees need calcium to survive and acid rain tends to lead to lower calcium levels in soil?
Objective
The correct answer will tell us about a difference between sugar maples and the other two kinds of trees that could lead to sugar maples being more likely to suffer from effects of calcium deficiency than are the other kinds of trees.
A
Soil in which calcium levels are significantly diminished by acid rain is also likely to be damaged in other ways by acid rain.
This doesn’t differentiate sugar maples from spruces and firs.
B
Sugar maples that do not receive enough calcium deteriorate less rapidly than spruces or firs that do not receive enough calcium.
This makes the discrepancy more difficult to explain, because it suggests sugar maples would be healthier than spruces and firs when they don’t get enough calcium. But sugar maples actually show more signs of decline.
C
Spruces and firs, unlike sugar maples, can extract calcium from a mineral compound that is common in soil and is not affected by acid rain.
This explains how spruces and firs can get more calcium than sugar maples, even when acid rain lowers levels of calcium in the soil. A non-soil source of calcium could lead to spruces and firs being less likely to suffer from calcium decline.
D
Sugar maples require more calcium in the spring and summer than they do in the fall and winter.
This doesn’t differentiate sugar maples from spruces and firs. We have no reason to think spruces and firs don’t have the same feature that this answer describes. So, we’re still left wondering why sugar maples are more likely to show signs of decline than the other trees.
E
Unlike spruces or firs, most sugar maples are native to areas that receive a lot of acid rain.
The stimulus compares sugar maples in forests that get a lot of acid rain with spruces and firs “in such forests.” So, we’re just talking about spruces and firs in forests that do get lots of acid rain.