Given this data, Jackson concludes that only Unknown 2 could be a protein. Which of the following explanations supports Jackson's conclusion?

Jackson performed an experiment in which he analyzed the elemental components of several unknown compounds. His results are shown in the table:

Jackson concludes that only Unknown 2 could be a protein.

Of the explanations that supports Jackson's conclusion is:

B. Proteins have some amino acids that contain sulfur, whereas most lipids, nucleic acids, and carbohydrates do not contain sulfur.