A researcher analyzes the mineral content of a particular grass and is surprised to find substantial levels of uranium in both leaf and root tissues. The most likely explanation for this finding is that

A) uranium is an essential nutrient for this grass.
B) the plant has a mutation in its active transport proteins.
C) there is a higher than usual concentration of uranium in the soil.
D) uranium is substituting for some other essential nutrient.
E) uranium is being supplied by mycorrhizae.