Please read: <br/><br/>1.In the 21st century, WHEN so many traditional values are disappearing, it is comforting to know that some still remain. <br/><br/>2.In the 21st century, so many traditional values are disappearing, it is comforting to know that some still remain. <br/><br/>3.In the 21st century, ON WHICH so many traditional values are disappearing, it is comforting to know that some still remain. <br/><br/>4.In the 21st century, THAT so many traditional values are disappearing, it is comforting to know that some still remain. <br/><br/>What sentences are correct? Please tell me the rule?<br/><br/>Thanks<br/><br/>Quoc