GWD4-14请教题目

Alexander浮云

Q14:
Guidebook writer:  I have visited hotels throughout the countryand have noticed that in those built before 1930 the quality of the originalcarpentry work is generally superior to that in hotels built afterward.  Clearly carpenters working on hotels before1930 typically worked with more skill, care, and effort than carpenters whohave 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.
   

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

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

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

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

我个人理解题目的意思是说writer说1930年以前建的旅馆里的木匠活的质量比那些在1930年以后建的的旅馆的要好，然后writer就说是因为1930年以前的木工拥有更多的技术，更用心跟努力才导致了这样一个结果

答案是选D，我不知道为什么D就是削弱writter的argument的。在我看来好像没有什么关系的样子。
所以在此请教下各位