All the biological macromolecules contain carbon, hydrogen and oxygen. however, most do not contain nitrogen. the category that contains nitrogen are:
a. lipids
b. proteins
c. carbohydrates
d. unsaturated fats.

b. Proteins

Explanation:

Amino acids are the substances that are bonded together in a specific sequence to make the polypeptide chains of proteins. All the 20 standard amino acids share a basic structure. All of them have a central carbon atom to which four functional groups are bonded. Three functional groups are common to all these amino acids. These common groups are carboxylic group, amino group (NH2) and a hydrogen atom. Therefore, all the proteins have "N" atoms in their structure. The last functional group is called the "side chain" that varies among different amino acids.

the answer would be 3

the scientific method.