Why Are Plants Such as the Pacific Yew Not Harvested

Why are plants such as the Pacific yew not harvested as extensively as they were in the past?

A) Nearly all Pacific yew plants have already been harvested.
B) The medically active ingredient can now be synthesized.
C) The active ingredient from Pacific yew is no longer effective.
D) Pacific yew plants have evolved to produce less of the active ingredient.
E) The relevant medical conditions are no longer a problem.