If X_it Is Correlated with X_is for Different Values of S

Multiple Choice

If X_it is correlated with X_is for different values of s and t, then

A) X_it is said to be autocorrelated
B) the OLS estimator cannot be computed
C) statistical inference cannot proceed in a standard way even if clustered standard errors are used
D) this is not of practical importance since these correlations are typically weak in applications