Critical Reasoning

Guidebook writer: I have visited hotels throughout the country and have noticed that in those hotels built before 1930 the quality of the original carpentry work is generally superior to that in hotels built afterwards. Clearly carpenters working on hotels before 1930 typically worked with more skils, care, and effort than carpenters who have worked on hotels built subsequently.

Which of the following, if true, most seriously weakens the guidebook writer's argument?

A) The quality of original carpentry in hotels is generally far superior to the quality of original carpentry in other structures, such as houses and stores
B)Hotels built since 1930 can generally accommodate more guests than those built before 1930
C)The material available to carpenters working before 1930 were not significant;y different in quality from the materials available to carpenters working after 1930
D)The better the quality of original carpentry in building, the less likely that building is to fall into disuse and be demolished
E)The average length of apprenticeship for carpenters has declined significantly since 1930.


I can't understand it.
Plus one more question I have the question writer has used comma (,) in "more skils, care, and effort" before "and". Is it necessary in this.


Answer is D as per OG 12