有一个农夫养了一群鸡。每次给鸡喂食的时候，他总是将栅栏门碰得很响。长时间以后，聪明的鸡们就得出这样一条因果律：栅栏门响过之后，主人必然会来喂食，因为以前总是这样的。
一日，友人来访。农夫为了款待朋友，准备杀两只鸡。他提着刀走进鸡场，照例把门碰得很响。两只公鸡坚信是主人喂食来了，仗着身强力壮，率先将脑袋伸出鸡笼。农夫手起刀落，两颗可怜的小脑袋来不及意识到它们的因果规律的无效，便流着鲜血落到了地上。

A. It is a sterile, abstract discipline, of little use in real life.
B. It is an essential element of persuasive discourse, but only one such element.
C. It is an important means of persuading people to act against their desires.
D. It is the lowest order of discourse because it is the less imaginative.