单选题 In paragraph 2 "leaner variables" and "strategies" are defined by reference to other writers ______.

A、 because these writers are authorities in the field and these are recognized as important concepts
B、 because these writers are authorities in the field and these are recognized as important definitions
C、 because the present author is not sure what these terms mean
D、 because the present author wishes to redefine the scope of research in this area

【正确答案】 B

【答案解析】由文章可知引用这两个词定义是因为作者是这一领域的专家。所以选B。