.net中的XPATH是1.0版本的，很多2.0中的函数是不兼容的，比如lower-case()、replace()函数等，下面中的XPATH语句在运行时会报错
//table[contains(lower-case(normalize-space(string()),'investment objective') and contains(lower-case(normalize-space(string())),'investment advisor')]
Namespace Manager or XsltContext needed. This query has a prefix, variable, or user-defined function.
只能用别的函数进行替换了translate(normalize-space(string()),'ABCDEFGHIJKLMNOPQRSTUVWXYZ','abcdefghijklmnopqrstuvwxyz')，修改后的语句可以成功运行！
//table[contains(translate(normalize-space(string()),'ABCDEFGHIJKLMNOPQRSTUVWXYZ','abcdefghijklmnopqrstuvwxyz'),'investment objective') and contains(translate(normalize-space(string()),'ABCDEFGHIJKLMNOPQRSTUVWXYZ','abcdefghijklmnopqrstuvwxyz'),'investment advisor')]