In the Study by Mayntz Et Al

In the study by Mayntz et al., wolf spiders were fed either a protein-rich or lipid-rich diet of fruit flies (Drosophila) and then tested for their preference by being presented with each diet in sequence. Which statement about the results of the study is true?

A) All spiders preferred protein because protein is both uniquely important and uniquely tenuous in animal nutrition (i.e., it is "foremost") .
B) All spiders preferred lipid because it has the most energy per gram.
C) Spiders on the protein-rich diet ate flies rich in protein and spiders on the lipid-rich diet ate flies rich in lipid.
D) Spiders on the protein-rich diet ate flies rich in lipid and spiders on the lipid-rich diet ate flies rich in protein.