Why is the answer 3 but not 4?

11. Which structure of protein is required for attaining enzymatic activity?
(1) Primary structure
(2) Secondary structure
(3) Tertiary structure
(4) Quaternary structure

Dear Student, Quaternary structure helps in determining the regulatory properties of a protein whereas tertiary structure helps in the enzymatic activity as tertiary structure can change its shape on the basis of conditions available which is very much needed for an enzyme to work. Regards