After a volcanic eruption has covered an area with lava, which of the following is the most likely order of succession in the re-population of the area? * lichens → grasses → shrubs → trees mosses → grasses → lichens → trees grasses → trees → mosses → lichens shrubs → grasses → trees → lichens

The choices for this question are:
A lichens →grasses →shrubs →trees 
B mosses →grasses →lichens →trees 
C grasses →trees →mosses →lichens 
D shrubs →grasses →trees →lichens

The correct answer is A. Lichens are able to survive in very harsh environments and would therefore be a suitable pioneer. Grasses would be suitable to succeed lichens as the lichens break down the larva rock into soil. After further breaking down of rock into soil by grass, shrubs will start to grow and these will be succeeded by trees as the ecosystem approaches maturity. 

A. mitochondrion b. nucleus