Possible answers:
+ weather;
+ heat;
+ magma;
+ rain;
+ streams;
+ water;
+ trees;
+ crust;
Given those answer options, answer the question: Fact 1: The looseness of soil has a positive impact on a plant 's roots' growth in that soil. Fact 2: Tree roots stabilize the soil and prevent soil erosion. Given the two facts above, what makes soil stable?
A:
trees