One Claim That Trade Barrier Proponents Use to Enforce Environmental

One claim that trade barrier proponents use to enforce environmental standards is that

A) environmental standards do not reduce industrial competitiveness and do not induce race-to-the-bottom, where countries are forced to rescind their standards in order to maintain employment.
B) high standards in industrialized nations motivates some firms to "export pollution" to developing countries by relocating their dirty industries.
C) enforcing environmental standards is essential, as there are no differences between labor standards and environmental standards.
D) all environmental impacts are non-transboundary.