Jackson performed an experiment in which he analyzed the elemental components of several unknown compounds. his results are shown in the table below.
elemental components of unknown compounds
carbon hydrogen nitrogen oxygen phosphorus sulfur
unknown 1 yes yes yes yes yes no
unknown 2 yes yes yes yes yes yes
unknown 3 yes yes no yes no no
unknown 4 yes yes no yes no no
given this data, jackson concludes that only unknown 2 could be a protein. which of the following explanations supports jackson's conclusion?