$1.$The height of the column based on the condition in the gas film is important for ensuring:

A$)$ Minimum solvent usage.

B$)$ Adequate contact time between the gas and the liquid phases.

C$)$ The structural stability of the column.

D$)$ Optimal temperature control.

$2.$If the operating conditions shift to favor the liquid film, how does this affect the design of the column in terms of NTU and HTU?

A$)$ NTU decreases and HTU increases, leading to a taller column.

B$)$ NTU increases and HTU decreases, requiring a shorter column.

C$)$ Both NTU and HTU increase, necessitating additional packing material.

D$)$ Both NTU and HTU decrease, allowing for a reduction in column height.