The Order of Integration A $\phi _ { 1 }$ In the Quasi Difference

Short Answer

The order of integration a. can never be zero.
b. is the number of times that the series needs to be differenced for it to be stationary.
c. is the value of $\phi _ { 1 }$ in the quasi difference $\left( \Delta Y _ { t } - \phi _ { 1 } Y _ { t - 1 } \right)$ .
d. depends on the number of lags in the VAR specification.