1、Disneyland in California (was the first Disney theme park,but today there are also) Disney World in Florida and Euro Disney outside Paris.
解析：
1）Disneyland in California was the first Disney theme park 中所以用过去时态是因为世界上除了Disneyland in California 之外,现在又在美国和海外陆续开了另外的5家,迪士尼乐园的唯一性已经成了过去.
2）but today there are also Disney World in Florida and Euro Disney outside Paris一句中有两个并列的主语Disney World in Florida 和 Euro Disney outside Paris.按理说,这种情况应该遵循就近一致的原则用there is,但是在实际使用中,如果有两个并列的主语,在美国英语中用are 也是常见现象.
基于上述分析,如果按严格的语法规定把可以将就使用的第二句的主谓一致改为 there is,那么第一句用现在时态 (is the first Disney theme park) 就成了严重的语法错误.根据避重就轻的原则,原句比起改为,sered tordayt.on why you u don' go swimming every day.B (is the first Disney theme park,but today there is also) 更为合理.
2、(During his presidency,John Quincy Adams,who was known for his formal nature,was often lonely and isolated.)
A.原句的结构为——
句子主体：
John Quincy Adams was often lonely and isolated.约翰·昆西·亚当斯常常是寂寞和孤独的
附加成分：
* 时间状语：During his presidency在他的任期内
* 定语从句：who was known for his formal nature,亚当斯因其拘谨的性格为人所知.
C 项结构为——
句子主体：
JQA was a president 约翰·昆西·亚当斯曾是个总统
附加成分：
* 伴随状语often lonely an isolated,（与他伴随在一起的是）寂寞和孤独的
* 时间状语：during his presidency 在他的任期内
* 定语从句：that was known for his formal nature as well as for being lonely and isolated.他的任期因其拘谨的性格以及寂寞和与世隔绝而为人所知.
显而易见,C 项有两处错误——
1、句首的often lonely an isolated和定语从句中的for being lonely and isolated 重复；
2、his formal nature和lonely and isolated指的是John Quincy Adams的性格和所处的状态,不可能是his presidency（任期）的.