Guidebook writer:  I have visited hotels throughout the country and have noticed that in those built before 1930 the quality of the original carpentry work is generally superior to that in hotels built afterward.  Clearly carpenters working on hotels before 1930 typically worked with more skill, 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?

1. 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.

2. Hotels built since 1930 can generally accommodate more guests than those built before 1930.

3. The materials available to carpenters working before 1930 were not significantly different in quality from the materials available to carpenters working after 1930.

4. The better the quality of original carpentry in a building, the less likely that building is to fall into disuse and be demolished.

5. The average length of apprenticeship for carpenters has declined significantly since 1930.

为什么是D?不明白。谁明白的给解释解释

我认为，题中强调Clearly carpenters working on hotels before 1930 typically worked with more skill, care, and effort than carpenters who have worked on hotels built subsequently，要削弱原因，就用他因削弱。D The better quality of original carpentry.即说明不是carpenters的技术造成。B说能住更多人，无关。

请指正

No, I'm sorry but I think you've missed the point of this question.

In this argument which says the carpenters before 1930 are better than those who in nowdays based on the performance of the architecture based on the comparison between the old hotel's delicate carpentry and the carpentry in nowdays bulding.

D says this comparison is not fair one since the author attempts to compare the best remainings with the buildings in nowdays.  It is not a peer to peer comparison.

So D almost questioned the validation of the logical thread rather than to find out an other reason to weaken it.