4. D。主旨题。主文主要介绍了这种水蜘蛛的生活情况，由此可知作者的目的是要读者了解水蜘蛛的特征，所以选D。
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Perhaps
the most famous theory, the study of body movement, was suggested by Professor
Ray Birdwhistell. He believes that physical appearance is often culturally
programmed. In other words, we learn our looks-we are not born with them. A
baby has generally informed face features. A baby, according to Birdwhistell,
learns where to set the eyebrows by looking at those around-family and friends.
This helps explain why the people of some areas of the United States look so
much alike, new Englanders or Southerners have certain common face features
that cannot be explained by genetics(遗传学).
The exact shape of the mouth is not set at birth, it is learned after. In fact,
the final mouth shape is not formed until well after new teeth are set. For
many, this can be well into grown-ups. A husband and wife together for a long
time often come to look alike. We learn our looks from those around us. This is
perhaps why in a single country area where people smile more than those in
other areas. In the United States, for example, the South is the part of the
country where the people smile most frequently. In New England they smile less,
and in the western part of New York State still less. Many southerners find
cities such as New York cold and unfriendly, partly because people on Madison
Avenue smile less than people on Peachtree Street in Atlanta. Georgia. People
in Atlanta, Georgia. People in largely populated areas also smile and greet
each other in public less than people in small towns do.
