Moss Invades and Establishes Itself on Bare Rock,accumulating the Beginnings

Multiple Choice

Moss invades and establishes itself on bare rock,accumulating the beginnings of soil.After several years,enough soil has become established that grasses begin to grow where there was once bare rock.Without the moss building up soil,the grasses would have had no chance.
-The establishment of the mosses on bare rock and eventual addition of grasses represents

A) a climax ecosystem.
B) primary succession.
C) secondary succession.
D) intermediate succession.