asp.net String.formatのカッコの入れ方

 
  
String.Format("{0} world!","hello") //    hello world！，    ，                      ： 
  
String.Format("{0} wo{rld!","hello") //        ，     ：Input string was not in a correct format. 
  
//    :String.Format("{0} wo{{rld!","hello") 
  
//or 
  
String.Format("{0} wo{1}rld!","hello","{") 
  
//       hello wo{rld!