可以用英文解释一下吗

问题如下：

Which of the following situations can linear regression be used to model the relationship between two time series?

选项：

Only one of two time series has a unit root.

Each time series has a unit root but they are cointegrated.

Each time series has a unit root and they are not cointegrated.

解释：

B is correct.

考点: Regression with More Than One Time Series & Summary.

解析：只有当两个时间序列都是平稳的，或者两个时间序列都不平稳，但他们是协整的，在这两种情况下我们是可以做回归分析的。两者有其一不平稳，或者两者都不平稳也不协整时，我们是不可以做回归分析的。所以只有B选项符合条件。