7. 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. @