there happened to be 还是there happen to be

把happen换成appear呢？

there are sth happened 还是there are sth happened ? there happened to be 还是there happen to be happened There happened to be a friend of mine in the hotel. There happened to be no one in your office when I phone 中文解释There's no need to refer to what happened last year; it's all water under the bridge now Joseph Heller -Something happened ________has happened to him? happened and happening What happened next? 这句话对吗？为什么要用happened