Following are certain statements regarding terpene class of secondary metabolites in plants:

A. Isopentenyl diphosphate and its isomer combine to form larger terpenes.

B. Diterpenes are 20 carbon compounds.

C. All terpenes are derived from the union of 4-carbon elements.

D. Pyrethroids are monoterpene esters.

Which one of the following combination of above statements is correct?