speak impromptu; make an impromptu (or extemporaneous) speech

• 即席讲话

speak impromptu; make an impromptu (or extemporaneous) speech的用法和样例：

例句

1. Ben hadn't prepared a speech, so he had to speak off the cuff.
   本没有准备演说，因此他不得不来个即席讲话了。
2. I spoke for an hour easily, and from that time always extemporized.
   我轻而易举地讲了一个钟头，从那以后我就总是即席讲话了。