$8.$ Continuous contact equipment such as packed columns are characterized by $\_\_\_$ flow of the phases, a large $\_$ area for mass transfer, and a $\_\_\_$ pressure drop.

$-$ a$)$ counter$-$current, contact, low

$-$ b$)$ co$-$current, surface, high

$-$ c$)$ parallel, volume, minimal

$-$ d$)$ random, interfacial, significant