Where does the sentence fit?

Question

Look at the four letters (**A**,**B**,**C**,**D**) that indicate where the following sentence can be added to following passage. This explains how, for example, alpine cushion plants have been found growing at an altitude of 6,180 meters.Where does the sentence fit?Above the tree line there is zone that is generally called alpine tundra. **A** Immediately adjacent to the timberline, the tundra consists of a fairly complete cover of low-lying shrubs, herbs, and grasses, while higher up the number and diversity of species decrease until there is much bare ground with occasional mosses and lichens and some prostrate cushion plants. **B** Some plants can even survive in favorable microhabitats above the snow line. The highest plants in the world occur at around 6,100 meters on Makalu in the Himalayas. **C** At this great height, rocks, warmed by the sun, melt small snowdrifts. **D**The answer is D, but I see that the choice C is also make sense. Could you please help me with this problem? Thank you so much!

Answer 1

"C" gives the reason why plants are able to grow in the high mountains -- they get water from the melting snowdrifts that are warned by the sun. The choice is logically "D" because "this" in "this explains" refers to the reason that was just given.