求助：GWD1-Q13，还是不明白！！！

In the United States, of the people who moved from one state to another when they retired, the percentage who retired to Florida has decreased by three percentage points over the past ten years.  Since many local businesses in Florida cater to retirees, this decline is likely to have a noticeably negative economic effect on these businesses.

Which of the following, if true, most seriously weakens the argument?

A.       Florida attracts more people who move from one state to another when they retire than does any other state.
B.       The number of people who move out of Florida to accept employment in other states has increased over the past ten years.
C.       There are far more local businesses in Florida that cater to tourists than there are local businesses that cater to retirees.
D.       The total number of people who retired and moved to another state for their retirement has increased significantly over the past ten years.
E.       The number of people who left Florida when they retired to live in another state was greater last year than it was ten years ago.

这个题之前有很多贴子讨论过了，我也明白了为什么答案是D。
我想问的是C为什么不对？原文的意思不是说因为many local businesses in Florida cater to retirees，那么既然retirees减少了，就退出了整个Florida经济就不景气了。C说的是别的local business很好，（也就是说不一定这个行业就是Florida的支柱产业），所以就不能说明整个经济的不景气啊~~~
我想知道我的理解哪里错了呢？