Under normal conditions, rocks composed of clay produce far less friction than do other rock types.
在正常情况下，由粘土组成的岩石产生的摩擦要比其他类型的岩石小得多。
2
Creative ideas not only produce their own instruments of survival as time and circumstances demand, but permit the substitution of new forms for old under the pressure of changed circumstances.
One site alone, the Pentland Firth, between Orkney and mainland Scotland, could produce 10% of the country's electricity with banks of turbines under the sea.