问题如下：
3.Based on the regression results in Exhibit 1, the original time series of exchange rates:
选项：
A.has a unit root.
B.exhibits stationarity.
C.can be modeled using linear regression.
解释：
A is correct. If the exchange rate series is a random walk, then the first-differenced series will yield b0 = 0 and b1 = 0, and the error terms will not be serially correlated. The data in Exhibit 1 show that this is the case: Neither the intercept nor the coefficient on the first lag of the first-differenced exchange rate in Regression 2 differs significantly from zero because the t-statistics of both coefficients are less than the critical t-statistic of 1.98. Also, the residual autocorrelations do not differ significantly from zero because the t-statistics of all autocorrelations are less than the critical t-statistic of 1.98. Therefore, because all random walks have unit roots, the exchange rate time series used to run Regression 1 has a unit root.
If the exchange rate series is a random walk, then the first-differenced series will yield b0 = 0 and b1 = 0, and the error terms will not be serially correlated. 如果原始数据存在单位根，那么它的一阶差分也就是 Regression 2中的B0和B1都会等于0，并且不存在自相关。可是为什么呢？为什么原始数据存在单位根，那它的一阶差分也就是 Regression 2中的B0和B1都会等于0？？？
