How should drivers of vehicles act on a narrow and steep road (sharp ascent)?

1. AWhoever arrived first will enter the narrow section first.
2. BIf necessary, the driver of the descending vehicle will stop his vehicle and allow the ascending vehicle to continue on its way.
3. CIt is enough if both of them keep to the edge of the road, in order to prevent a collision.
4. DIf necessary, the driver of the ascending vehicle will stop his vehicle and allow the descending vehicle to continue on its way.

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