Answer:
If two vehicles meet on a narrow mountain road in which there is only room for one vehicle to travel at a time, the vehicle going downhill must yield to the vehicle traveling uphill.
Step-by-step explanation:
If two vehicles meet on a narrow road and it is impossible for both of them to pass at the same time, the vehicle facing uphill has the right-of-way. The right-of-way is the right of traffic to take precedence over other traffic participants. The vehicle facing downhill should back up until it's possible for the other vehicle to pass, as it has better control when backing up. This rule should always be followed unless it's for some reason more practical for the vehicle going uphill to find a turnout or wider space.