People have wondered for a long time how their personalities and behavior are formed. It is not easy to explain why one person is intelligent and another is not, or why one is cooperative and another is competitive. 
Social scientists are of course extremely interested in these types of questions. They want to explain why we possess certain characteristics and exhibit certain behavior. There are no clear answers yet, but two distinct schools of thought on the matter have developed. As one might expect, the two approaches are very different from each other, and there is a great deal of debate between proponents of each theory. The controversy is often conveniently referred to as “nature and nurture”．
Those who support the “nature” side of the conflict believe that our personalities and behavior patterns are largely determined by biological factors. That our environment has little, if anything, to do with our abilities, characteristics and behavior is central to this theory. Taken to an extreme，this theory states that our behavior is predetermined to such a great degree that we are almost completely governed by our instincts(本能)．
Proponents of the “nurture” theory, or, as they are often called, behaviorists, claim that our environment is more important than our biologically based instincts in determining how we will act. A behaviorist, B. F. Skinner, sees humans as beings whose behavior is almost completely shaped by their surroundings. The behaviorists' view of the human being is quite mechanistic. They state that, like machines, humans respond to environmental stimuli (刺激) as the basis of their behavior. 
Socially and politically, the consequences of these two theories are far-reaching. In the US，for example, blacks often score below whites on standardized intelligence tests. This leads some “nature” proponents to conclude that blacks are genetically lower in status than whites. Behaviorists, on the contrary, say that the differences in scores are due to the fact that blacks are often robbed of many of the educational and other environmental advantages that whites enjoy, and that, as a result, they do not develop the same responses that whites do.
Neither of these theories can yet fully explain human behavior. In fact, it is quite likely that the key to our behavior lies somewhere between these two extremes and that the controversy will continue for a long time is certain. 
This passage is mainly concerned with ________.

A．relation between personality and behavior

B．relation between behavior and environment

C．different accounts of patterns of human behavior

D．different theories of the formation of human behavior

The underlined word “proponents” in Paragraph 2 means ________.

A．creators

B．advisors

C．advocates

D．judges

In Paragraph 5, the author mainly writes about ________.

A．the considerable influence of the two theories

B．differences between the blacks and whites

C．racial discrimination in the United States

D．different responds to intelligence tests

What's the author's purpose in writing the passage?

A．To call our attention to the changes of human behavior.

B．To urge scientists to do more research in social science.

C．To give us a detailed explanation of human behavior.

D．To present an argument in the field of social science.