At an enormous research cost, a leading chemical company has developed

At an enormous research cost, a leading chemical company has developed a manufacturing process for converting wood fibers into a plastic. According to the company, this new plastic can be used for, among other things, the hulls of small sailboats. But what does the company think sailboat hulls used to be made of? Surely the mania for high technology can scarcely go further than this.

conclusion - this new plastic is a waste of technology aka has no advantae.

Which of the following, if true, would most seriously weaken the author’s conclusion?
Pre thinking - any option that shows these new plastics do give an advantage or has a better use.
REMEMBER TO PICK BEST 100% weaken

(A) The plastic produced by the process is considerably lighter, stronger, and more watertight than wood. - Correct - shows an advantage.
(B) The wood used in producing the plastic is itself in increasingly short supply. - This strengthens the author's conclusion.
(C) The cost of the manufacturing process of the plastic increases the cost of producing a sailboat hull by 10 to 15 percent. irrlevant
(D) Much of the cost of the research that developed the new process will be written off for tax purposes by the chemical company. irrelevnt
(E) The development of the new plastic is expected to help make the chemical company an important supplier of boat-building materials. - Reject - The word 'expected' is not clear if its a really good innovation.

Answer option A is correct.

Let us take a look-
The question stem says the following:
(a) New whatever type of plastic
(b) A particular possible use of the new plastic
(c) Author's rhetoric indicating plastic was already in use in case of (b) and new plastic is only hype.
One thing to note is that the company is only suggesting a possible replacement which the author believes is not required because we already have one material in use and it is unnecessary technological hype to think new plastic can replace old plastic.

To weaken the author's argument, we need to attack his/her argument that using the new material is pointless. To do this, we can try to prove that using the new plastic is better than using the existing material.

(A) The plastic produced by the process is considerably lighter, stronger, and more watertight than wood.
Seems to provide a reason in favor of the new material. Probable answer since it weakens author's retort.

(B) The wood used in producing the plastic is itself in increasingly short supply.
This casts doubt about viability of the new plastic. Also, w.r.t. the author's argument, this is entirely unrelated since author is not questioning future viability but the use of the material in small sailboat hulls.

(C) The cost of the manufacturing process of the plastic increases the cost of producing a sailboat hull by 10 to 15 percent.
This is a disadvantage of using the new material. Hence, (C) strengthens rather than weakens the author's argument. It is also not exactly related the argument as it is talking about cost while the author is mocking the possibility of its use itself.

(D) Much of the cost of the research that developed the new process will be written off for tax purposes by the chemical company.
Not being taxed doesn't automatically mean it will be cheaper. Since superiority of new plastic in any manner is not established, eliminate.

(E) The development of the new plastic is expected to help make the chemical company an important supplier of boat-building materials.

This is entirely out of scope as it is not relevant to any aspect of the question.

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