【单选题】

The primary purpose of the passage is to
A．(A) describe in detail how the principles of homeostasis apply to living things

B．(B) propose a modification in the most widely accepted theory of homeostasis
C．(C) compare and contrast the role of positive and negative feedback in maintaining various applied systems
D．(D) discuss the concept of homeostasis in the abstract and relate some of its most important principles
E．(E) provide examples of systems which are ruled by the principle of homeostasis