https://online2.tingclass.net/lesson/shi0529/0009/9907/624.mp3
https://image.tingclass.net/statics/js/2012
讲解文本：
rack one's brain 绞尽脑汁，努力思索
Write them down and then you won't have to rack your brain anymore!
把这些都写下来，你就不用每次都拼命想了。
The test is too hard. I have been racking my brain for days.
这个测试太难了，我已经绞尽脑汁想了几天了。
