Questions 21 to 25 are based on the following passage.
Every artist knows in his heart that he is saying something to the public. Not only does he want so say it well，but he wants it to be something which has not been said before. He hopes the public will listen and understand-he wants to teach them. and he wants them to learn from him. What visual artists like painters want to teach is easy to make out but difficult to explain，because painters translate their experiences into shapes and colors，not words. They seem to feel that a certain selection of shapes and colors，out of the countless billions possible，is exceptionally interesting for them and worth showing to us. Without their work we should never have noticed these particular shapes and colors，or have felt the delight which they brought to the artist. Most artists take their shapes and colors from the world of nature and from human bodies in motion and repose：their choices indicate that these aspects of the world are worth looking at，that they contain beautiful sights. Contemporary artists might say that they merely choose subjects that provide an interesting pattern，that there is nothing more in it. Yet even they do not choose entirely without reference to the character of their subjects. If one painter chooses to paint a gangrenous(生坏疽的)leg and another a lake in moonlight，each of them is directing our attention to a certain aspect of the world. Each painter is telling us something，showing us something，emphasizing something-all of which mean that，consciously or unconsciously，he is trying to teach us.
All artists are common in that______.
A. they use shapes and colors instead of words
B. they are trying to teach the public
C. what they want to teach is difficult to explain
D. they want to learn from the public