這句中的most 是甚麼意思？

最昂貴= the most expensive , 不等於 most expensive, so if there is only 2 options, it must be the later one.

2013-12-06 19:29:42 補充：
But it seems that this is not working quite well, and it is a serious grammar mistake. If you had not made up this sentence, you had better consider carefully to ensure that everything is right. In this case, if in exam, you had better choose the second one. If else, you had better check it again.

這句嚴格來說，grammar 有錯，因為 superlative 前面是要加上 the most，而非只是 most。

不過，如果 most 不是用來表示 superlative，就不需要 the，如:
Most students are hard-working.
I love him most.

希望幫到你。

2013-12-06 19:30:36 補充：
第一句的 most 表示“大部分“

第二句的 most 表示“最“，但並非如你這句指 superlative