Look at the representation of a hillside below. The symbols in each stratus of the cross-section represent fossils of different organisms. Which of the following organisms must have evolved first?

% * ^ ^ *

% $ $ $ # # # * * * * *

$ * * * $ $ # # # # @

% # # # @ @ ! ! ! ! * *

@ < < < < < + + + + = =

A*

B#

C@

D$