If your remarks are extemporaneous, you have not prepared them in advance.

如果你的发言是即席的，说明你没有事先。

At the Academy's annual Summit, Jobs gave a couple of short, extemporaneous talks to a roomful of promising young high school students.

在学的年度峰会上，对一屋子前途无量的年轻高中生做了几次简短的即席演讲。