Although the suspected carcinogen dioxin is formed when lignin......

A) Sorting garbage would allow recovery of recyclable materials as well as prevent dioxin formation. - does not weaken the argument.
B) Incineration of plastics is suspected of causing emissions of several dangerous pollutants. - the passage deals with dioxins. ''pollutants'' are out of scope in reference to the this passage.
C) The level at which dioxin concentrations become unacceptably high is still a matter of dispute within the scientific community. - if anything, this would tip the argument in favor of the position taken by the author. Besides, acknowledging that a dispute regarding the 'level' that is considered unacceptable exists is itself not sufficient to weaken the argument.
D) Existing incineration technology leaves residues containing sufficient amounts of lignin and chlorine for dioxin formation after burning. - From (D), we know that even with the existing incineration technologies, the threat of dioxins still looms from the left overs of the burning process. Hence, (D) weakens the argument. Therefore, (D) is the right answer choice.
E) Lignin and chlorine are found in other substances that might be burned in a garbage-disposal plant as well as paper and plastic. - (E) tells us that there are different sources of lignin. Still, acknowledging this fact is not proof that the current incineration technology is insufficient. Hence, (E) does not weaken the argument.

Hi egmat, i'll appreciate your help with my analysis.

I used the following process to identify the conclusion, since I consider that question stem is not specific enough to work with it.
Is A because of B? or Is B because of A?

My two options were:
(A) Advocates of garbage disposal through burning maintain that separating garbage is impractical and unnecessary.
(B) They claim that high-temperature incineration will destroy the ingredients needed for production of dioxin.

In my opinion, A because of B is more logical than B because of A:

Advocates of garbage disposal through burning maintain that separating garbage is impractical and unnecessary because they claim that high-temperature incineration will destroy the ingredients needed for production of dioxin.

Since the process to identify the conclusion is crucial to choose the correct the answer choice, Would you agree with my analysis?

If i'm not wrong above, I think choice A would be a better answer choice since A attacks directly the conclusion.

My assumption would be that separating garbage is impractical and unnecessary if it does not prevent dioxin formation. That's exactly what choice A states, isn't it?

Choice D would be correct if the conclusion were “ They claim that high-temperature incineration will destroy the ingredients needed for production of dioxin.”

Thanks a lot!