When Marx was in London, he _______ read at the library for hours.
The people, _______ had been damaged by the flood, were given help by the Red Cross.
This is a simple idea, but that is hard to put into practice.
– Who is the man standing there?– If you know, his name is Mike.
One solution to this problem now is sustainable development.
Wind power units are placed ______ there is a lot of wind.