This question and its explanation is kind of confusing. The question talks about weakening argument and answer D, as explained in OG, makes a little sense. Has anbody gone through this?

I mean How this secret can weaken the argument that "better quality of carpentary is good for building's future?" This is pretty obvious and that is said in argument through comparison of the quality of work in two different era; before 1930 and after 1930. This explanation actually SUPPORT the argument. This does not weaken the argument and question ask about weakening.