如从字符串this is an apple删除aeiou字符

输出:ths s n ppl

具体代码：
static string RemoveChars(string str, string remove)  
{   
         if(string.IsNullOrEmpty(str) || string.IsNullOrEmpty(remove))  
         {  
                   throw new ArgumentException("....");  
         }  
 
         StringBuilder result = new StringBuilder(str.Length);  
 
         Dictionary<char, bool> dictionary = new Dictionary<char, bool>();  
 
         foreach(char ch in remove)  
         {  
                   dictionary[ch] = true;  
         }  
 
         foreach(char ch in str)  
         {  
                   if(!dictionary.ContainsKey(ch))  
 
                   {  
                            result.Append(ch);  
                   }  
         }  
 
    return result.ToString();  
}