7.(Whatever) the reasons may be ...不管什么; 没有其他选择不能用whichever
8.At (what is called Hilton Hotel.) 在一个叫 "Hilton Hotel" 的所在,如果改为问句就比较容易能 理解了 ：What is the name of the hotel you checked in yesterday?What ...（is the name) 道理相同
9....B.what was so called ...
和上题解释一样,改成问句试试看：What did people call this creature that was found in the mountain?
10.A./;a sending us fresh vegetables .done us a great service
新鲜多样的蔬菜,没特别指单一一个或一种所以不需冠词; 为我们提供了一个极好的服务.
11.A.a;a In a world where ...意思是说在一个 ...的特殊环境中,毕竟不是全人类都处于这种状态下.
12.C./;the National Day 单指国庆那天（即便十一节也放长假）,春节 Spring Festival 这个 Festival 涵盖了整个假期.
13.A./;the north of (the) Philippine Islands,座落于菲律宾群岛的北方.Philippine Islands 是专有名词前面必须加冠词,north 只说明方位,紧跟small town 直接形容它.
希望能对你的学习带来一些帮助.