Columnist: There are certain pesticides that, even though they have be

Pesticide ABC is used for corn crops and is banned from using for 30 yrs.
Pesticide ABC is currently manufactured in US and exported to China.
China uses ABC on corn, uses half of it domestically and exports the other half to US.

Conclusion: This trade causes health risks to US consumers as well as to Chinese consumers.
Which one of the following, if true, most seriously weakens the columnist’s argument?

(A) Trace amounts of some of the pesticides banned for use in the United States can be detected in the soil where they were used 30 years ago => "Amounts of ABC (used 30 yrs ago) found in soil" is irrelevant and doesn't impact conclusion at all.

(B) Most of the pesticides that are manufactured in the United States and exported are not among those banned for use in the United States => We are only talking about some certain pesticides (e.g. ABC) that ARE BANNED but STILL MANUFACTURED and EXPORTED.

(C) The United States is not the only country that manufactures and exports the pesticides that are banned for use in the United States =>

ONE WAY TO WEAKEN A CAUSE-EFFECT ARGUMENT IS TO INTRODUCE AN ALTERNATIVE CAUSE FOR THE SAME EFFECT.
If X -> Y
Possible weakener: Z -> Y (So X may or may not cause Y).

In this case,
Mexico also manufactures pesticide ABC and exports it to China.
So the trade between US and China may result in health risk to US consumers (and chinese consumers) but the trade between Mexico and China can cause health risks.

(D) The banned pesticides pose a greater risk to people in the countries in which they are used than to U.S. consumers => Comparing "health risks to people in China and health risks to people in US" does not impact our conclusion.

(E) There are many pesticides that are banned for use in other countries that are not banned for use in the United States => Other pesticides banned for use in China and are not banned for use in US is out of scope.

Columnist: There are certain pesticides that, even though they have been banned for use in the United States for nearly 30 years, are still manufactured there and exported to other countries. In addition to jeopardizing the health of people in these countries, this practice greatly increases the health risk to U.S. consumers, for these pesticides are often used on agricultural products imported into the United States.

Which one of the following, if true, most seriously weakens the columnist’s argument?

(A) Trace amounts of some of the pesticides banned for use in the United States can be detected in the soil where they were used 30 years ago

(B) Most of the pesticides that are manufactures in the United States and exported are not among those banned for use in the United States

(C) The United States is not the only country that manufactures and exports the pesticides that are banned for use in the United States

(D) The banned pesticides pose a greater risk to people in the countries in which they are used than to U.S. consumers

(E) There are many pesticides that are banned for use in other countries that are not banned for use in the United States

The core of the passage is why columnist says that the practice of exporting pesticides and importing of agricultural products leads to health risk to US consumers. It could be that there are other factors that leads to such conclusion or a reverse case.

A altogether gets into something else that is irrelevant. Why that export-import practice may not lead to health risk but something else is what we are looking for.
B looks fine but some, even if only pesticide, still lead to health risk thus strengthening columnist argument. But we can keep it for relative comparison.
D again like A goes offtrack. Not concerned about comparison and most importantly it still leads to health risk.
E is dumb among the choices.

C is like yes its the case wherein US imports but these imports agricultural products that are manufactured in other countries, possibly using in-house manufactured pesticides. So, in a way the argument that practice of US manufacturing pesticides and importing agricultural products leads to health risk is somewhat weakened, if not fully. C basically, considers a partial scope and moulds it to make it different. NOT the best of answer one might be looking for.

Answer C.

Conclusion - the pesticides banned by US are still exported by the US to some countries who use these pesticides and export agricultural products back to US- GREATLY INCREASING HEALTH RICK IN THE USA.

WEAKENING possibilities- 1. the products received by US have not been damaged by the pesticides OR 2. SUCH EXPORTS ARE NOT CAUSING IN THE IMPORT OF HARMFUL PRODUCTS.

A) irrelevant
B) talks about other pesticides not the ones in question irrelevant
C) Correct - as per the 2nd weakening possibility - other countries will still export these banned pesticides making contribution of US exports insignificant in increasing health risk in US.
D) we are not concerned with health risk in other countries as per the conclusion.
E) again talks about pesticides that are not concerned in the question irrelevant.