replication data里文件里要求装backup和backto的包来备份变量的不同版本，但是网站打不开装不上，请问有替代方法吗？
*Install "backup" and "backto" ado files, which create backed up versions of variables
net from http://home.gwu.edu/~bartels/stata
*install 'backto' and 'backup' by clicking on them