Let me change the bag for you, to a clean one. Otherwise, this one is dirty, you might throw it away thinking it's garbage.

我帮你换袋子、换干净的，不然这样脏脏，你看到会当作垃圾丢掉。

youdao

Here's what I do. I change-- oops! Let me do that this way-- I change last to here, and keep first there, and I throw away all of that. All right?

接下来，我来改过来,此时这里是last，first位置没变,把这些都擦掉，好？

麻省理工公开课 - 计算机科学及编程导论课程节选