Answer:
A. grasses begin to grow in soil with organic matter
B. tress begin to grow in thick rich soil
C. mosses begin to grow in thin rocky soil
D. lichens begin to cover bare rock
It would be B. because that comes last.
Step-by-step explanation:
Whenever a volcano erupts, it puts a layer of rock over everything. Basically, over years and years, lichens will start growing and breaking down the rock. A bunch of years later, mosses will begin to grow in the "soil" that the lichens broke down. When the rocky dirt becomes actual dirt, grasses will start to grow. After that shrubs, and then trees.
Hope this helped! :)