问题如下：
8. Based on Exhibit 5, for which company would the regression of stock prices on oil prices be expected to yield valid coefficients that could be used to estimate the long-term relationship between stock price and oil price?
选项：
A.Company #1
B.Company #2
C.Company #3
解释：
B is correct. When two time series have a unit root but are co-integrated, the error term in the linear regression of one time series on the other will be covariance stationary. Exhibit 5 shows that the series of stock prices of Company #2 and the oil prices both contain a unit root, and the two time series are co-integrated. As a result, the regression coefficients and standard errors are consistent and can be used for hypothesis tests. Although the cointegrated regression estimates the long-term relation between the two series, it may not be the best model of the short-term relationship.
Exhibit 5 shows that the series of stock prices of Company #2 and the oil prices both contain a unit root, and the two time series are co-integrated.
请问 如何通过Exhibit 5 看出来他们含有单位根？
