sentence: Smoke from cigars permeated the lounge but the air was clear in the hall, as the 
complete: lounge permitted smoking.

sentence: Samantha was a positive person, while Victoria was always in a bad mood, so 
complete: Victoria scowled at everyone.

sentence: rhododendrons are easy to prune but  roses are not because the 
complete:
rhododendrons are very good natured.