The speaker suddenly changed tack and left us all rather confused.
演讲人突然改变了论调，把我们都搞糊涂了。
I hammered a tack into the wall and hung a small picture from it.
我在墙上钉了一个图钉，然后在上面挂了一张小图片。
My mother tacked the sleeves on before sewing them.
我妈妈在把袖子缝好之前，先用大针脚把它缝好。
