逻辑

chasedreamsrr

　　18.The average age of chief executive officers （CEO's） in a large sample of companies is 57. The average age of CEO's in those same companies 20 years ago was approximately eight years younger. On the basis of those data, it can be concluded that CEO's in general tend to be older now.Which of the following casts the most doubt on the conclusion drawn above?

　　（A） The dates when the CEO's assumed their current positions have not been specified.
　　（B） No information is given concerning the average number of years that CEO's remain in office.
　　（C） The information is based only on companies that have been operating for at least 20 years.
　　（D） Only approximate information is given concerning the average age of the CEO's 20 years ago.
　　（E） Information concerning the exact number of companies in the sample has not been given.

为啥选C啊？

francoisyang

所选取的公司现在的CEO平均年龄57，20年前这些公司的CEO平均年龄49。这些公司都是运营超过20年的公司，而20年前还有很多其他公司没被统计进去。所以不能说现在的平均年龄老。