Alkaloids Are Considered "Expensive" Defense Compounds to Produce Because They

Alkaloids are considered "expensive" defense compounds to produce because they:

A) contain a lot of carbon, which is costly for plants to concentrate.
B) vaporize readily, so they constantly have to be synthesized.
C) contain nitrogen, an essential and often limiting element plants need.
D) often function in very small concentrations.
E) contain proteins, which are very costly for a plant to produce.