As you travel up into the mountains, you notice discomfort in your ears. This is due to ...
Athe low pressure in your ears.
Bthe low pressure at the bottom.
Cthe low pressure in the mountain.
Dthe high pressure in the mountains.
Athe low pressure in your ears.
Bthe low pressure at the bottom.
Cthe low pressure in the mountain.
Dthe high pressure in the mountains.