What do nitrogenous substances typically comprise?

Nitrogenous substances are primarily defined by the presence of nitrogen in their molecular structure. This key characteristic distinguishes them from other organic compounds. In biological contexts, nitrogen is essential for the formation of amino acids, nucleotides, and other compounds critical for life. For instance, DNA and RNA, which are vital genetic materials, include nitrogenous bases that contain nitrogen.

While the other options include elements that might be found in various biological molecules, they do not specifically characterize nitrogenous substances. Carbon and oxygen, for example, are basic building blocks of many organic molecules but do not emphasize nitrogen's role. Similarly, hydrogen and sulfur are present in some biological compounds but do not define nitrogenous substances, and phosphorus, while significant in its own right (especially in nucleic acids), does not contribute to the definition of nitrogenous compounds. Thus, the emphasis on nitrogen as the primary component is what makes the correct answer stand out.