Translation of Kraft-Wärme-Kopplung

In England, a man would still open a door to a woman, but in other countries this habbit is less common. In a way, habits that existed hundred years ago slowly loose their meaning and importance.
However, the option of creating new lessons with multiple answers is now widely used by our users (teachers and students). However, we believe rather in context and single answers ant not multiple options.
We walked by waterfalls and rivers, but the water was too cold to swimm in. The hike made us tired and we were in the valley, which meant that we had to climb up again. The climb was difficult.