不知道指的是啥意思，請知道的人幫我解釋一下
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更新1:
With a light economic calendar, a financial panic just out of the way and an important Federal Reserve meeting just ahead, some investors may choose this week to ponder how much has changed, or not, since that awful day on Wall Street, Oct. 19, 1987, when the stock market fell more than 20 percent.