本视频先介绍了马克吐温的《卡拉维拉斯著名的跳蛙》和他的趣闻逸事，然后介绍了定语从句的用法。

This video starts with an introduction to The Celebrated Jumping frog of Calaveras County and Mark Twain’s anecdotes. Then it introduces the grammar about relative clauses with which and that.