重点讲解：
1. off the top of one's head
不加思索地；来不及思索地；
eg. It was the best I could think of off the top of my head.
这是我一时所能想到的最好的办法。
eg. Jane can tell you the correct amount off the top of her head.
简可以一下子把准确的数量告诉你。
2. on one's own
独立地；依靠自己地；
eg. John quit his job and struck out on his own as a traveling salesman.
约翰辞掉工作去做旅行推销员，独立闯新路。
eg. I'm well able to manage on my own.
我完全能够独自处理。
3. quite a bit
相当多，很多；
eg. He has got quite a bit salted away .
他攒了不少钱。
eg. He has knocked about quite a bit.
他经历过很多漂泊不定的生活。
