将We often see him dance改为被动语态

正确答案是：
He is often seen to dance by us.
注释：
see sb.do sth.的被动语态要加“to”,即：be seen to do sth.
另外,原句有often,只能改成：be seen to do sth.的形式,不能用be seen doing sth.
若原句是“We see him dancing now.”,被动语态才用：He is seen dancing by us now.