答案：C.
翻译：世博会提供了如此多的乐趣,以至于大多数参观者在全部看完之前就耗光了时间.
解释：
1. 此题考查so...that...句型的倒装.
该句型规定如下：把so所修饰的形容词（及该形容词修饰的名词）或副词提前至句首,并将主句部分倒装（即类似于一般疑问句变化,把be/助动词/情态动词提前）,而that从句句序不变.
2. 即该题的正常句序为：
The World Expo offered so much of interest that most visitors simply ran out of time before seeing it all.
把so much of interest提前,并紧跟助动词did,后面使用动词原形offer,即变成：
So much of interest did the World Expro offer that most visitors simply ran out of time before seeing it all.
3. 不过,楼主句中可能漏打了单词,so much of interest不通顺,不过并不影响做题.