GMAT Critical Reasoning (CR) | Re: No nation in the world has experienced as significant a

No nation in the world has experienced as significant a decline in its Yucaipa tree population as our nation. Yet only our nation imposes a law prohibiting the use of Yucaipa tree-bark oil in cosmetics. The purpose of this law in the first place was to help maintain the Yucaipa tree population, at least in this nation. But the law is clearly unnecessary and therefore should be repealed.

Which of the following, if true, would most seriously weaken the conclusion drawn in the passage?

a. This