What constitutes "evidence"?

I narrowed the answer choices down to (E) and (C) and chose (E), largely because the commentary on previous Argument Structure questions indicated that a statement like, "The greatest expense in irrigated agriculture is in pumping the water..." as found in the stimulus is not 'evidence' because it is simply a statement that the author posits to be true, rather than something like the results of a survey/experiment. So, when can a statement be considered 'evidence' in a question? Am I to understand that 'evidence' is much like 'phenomenon' on the LSAT in that the general definition of the word should be used rather than the more common, specific definition? In other words, in the same way that 'phenomenon' on the LSAT simply means "a thing/an instance of something", 'evidence' means "a support of a conclusion/premise"?