busy后面跟todo还是doing,膝盖后面的腿窝筋痛

busy的用法:be busy with sth和be busy doing sth的用法
辨析used_to_do_be_used_to_doingbe_used_to_doppt
used to do和be used to doing
辨析used to do be used to doingbe used to doppt
busy后面跟todo还是doing