How to print different html strings based on the class of an element

How do I write PHP code to the effect of:
If this article element contains the class "A" (some Wordpress function will be involved and its output queried here - the one that retrieves the classes for the current article - can you tell me what goes here if you know?), then print "this html string",
otherwise if it contains class "B", then print "that html string",
otherwise if it contains class "C", then print "this other html string".