Some people argue using ____________ nature to meet our own needs may spell disaster, unless we start to look around and understand how _________ clean environment benefits us all.

A．/; a

B．the; the

C．the; a

D．a; a

上图是美国施图茨的研究成果——交际活动与距离的关系图，根据这副图，我们可以得出两点结论？