21.  A great musician and much admired teacher, Nikolayeva knew what she was talking about.

22.  A gun is known to fire bullets at precisely three hundred and thirty meters per second.

23.  A knife-point poked into his back every few seconds, so he knew that the mestizo was close behind him.

24.  A language she once knew but had forgotten about, forgotten ever hearing, forgotten she could speak.

25.  A larger problem is that the flat tax would work havoc in the national economy, and nobody knows what to expect.

26.  A layer of gases, including those which are known as the greenhouse gases, surrounds the Earth.

27.  A legal scholar of considerable merit, he was a very private man, difficult to get to know and to describe.

28.  A man among men knows how to murder.

29.  A man is much better known through painting than through photography.

30.  A man stopped me in the street and asked if I knew where the theatre was.