Recent U.S. legislation limiting the emissions permissible

Recent U.S. legislation limiting the emissions permissible from automobiles will require auto manufacturers to incorporate new technology and more costly components in cars. This will drive up the price of cars, both at home and abroad. Therefore, the legislation will result in the loss of many export markets. The argument is most seriously weakened by which of the following?

A. Most of the countries to which U.S. automobiles are exported have recently enacted similar legislation limiting emissions.
B. Non-compliance with the new legislation can be punished with high fines.
C. Training factory workers to use the new technology required to manufacture compliant automobiles will be expensive and time-consuming.
D. Some automobile manufacturers will choose to relocate their plants to other countries that do not have stringent emissions standards.
E. Environmental groups have been leaning heavily on the auto industry to voluntarily institute such emissions standards.

GROCKIT Explanation:
This question’s conclusion—that the emissions standards legislation will result in the loss of many export markets for cars—rests on the assumption that the U.S. cars will become too expensive to be competitive in those markets. However, if other countries have recently enacted similar legislation, then the costs of domestic automobiles in those markets are likely to increase as well, which would allow the U.S. exports to raise their prices without becoming too expensive to sell.
A. This is the credited response. If many markets to which the U.S. exports cars have enacted similar legislation, it is likely that the costs of their domestic autos have increased as well, which might be sufficient to keep U.S. prices competitive even as those prices increase.
D. The possibility of auto manufacturers relocating their plants has NO EFFECT on the conclusion of the argument.

I agree with the OA.

But, as per choice (D), relocation to countries with no stringent standards by SOME manufacturers will definitely not drive up prices of SUCH manufacturers. Hence, this will not result in the loss of SOME (if not MANY) export markets. So, this WEAKENS the argument, at least to SOME extent. Definitely not as much choice (A) does.
But why does the explanation of choice (D) say that it has NO EFFECT on the conclusion of the argument? Am I missing something in the structure of the argument itself?

Many thanks & kudos are on their way