[单项选择]

Americans today believe that acceptable social behavior follows effortlessly from personal virtue. The (1) between morals and manners has become blurred. (2) you need is a good heart, most people assume, and the (3) will take care of itself. You don’t have to write thank-you notes.
Many Americans believe that natural behavior is beautiful. The "natural" (4) to human relations presumes that to know any person well enough is to love him, that the (5) human problem is a communication problem. This (6) that people might be separated by basically, generally irreconcilable differences--philosophical, political, or religious--and assumes that all such differences are (7) misunderstandings.
Indeed, it has never been easier to insult people inadvertently. A gentleman opens a door for a lady because his mother taught him that ladies (8) such courtesies, but she (9) and spits in his eye because he
A. essential
B. last
C. same
D. only