A homogeneous azeotropic distillation process separates an azeotropic $AB$ binary feed using a heavy entrainer, $E$, as shown in the figure. The loss of $E$ in the two product streams is negligible so that $E$ circulates around the process in a closedcircuit. For a distillation column with fully specified feed(s), given operating pressure, a single distillate stream and a single bottoms stream, the steady-state degrees of freedom equals $2$. For the process in the figure with a fully specified $AB$ feed stream and given column operating pressures, the steady-state degrees of freedom equals
- $3$
- $4$
- $5$
- $6$