同时查阅了then的用法,参555题:One noted economist has compared the Federal Reserve to an automobile racing through a tunnel, bouncing first off one wall, then the other; the car may get where it is going, but people may be hurt in the process. 此句中的then之前也未加and,而意思上是应该加and的,所以,由此看来,这个错误并非是一个致命错误。