Translation of beistellen

He also told me that he had build his scooter by himself. I could not understand how a doctor was able to build such a machine on his own. It seems that the circumstances made people capable of many things.
Every school has some narrow minded teachers who are not willing in investing in progressive educational process. They do not grasp that schooling methods today are different from last century's methods.
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.