I think C is the correct one
Pivot mean the central point, pin, or shaft on which a mechanism turns or oscillates.
The correct version of these two sentences when combined is:
When we were in Europe on vacation, we usually flew on airplanes: however, sometimes we took the train.
We apply the semi-colon to indicate that they have different ideas, and that they are clauses being joined into one sentence.
It looks like a log cabin so the closest is wickipup or longhouse
