The field of medicine has always attracted its share of quacks and charlatans — disreputable women and men with little or no medical knowledge who promise quick cures at cheap prices. The reasons why quackery thrives even in modern times are easy to find.To begin with, pain seems to be a chronic human condition. A person whose body or mind "hurts" will often pay any amount of money for the promise of relief. Second, even the best medical treatment cannot cure all the ills that beset men and women. People who mistrust or dislike the truths that their physicians tell them often turn to more sympathetic ears.Many people lack the training necessary to evaluate medical claims. Given the choice between (a) a reputable physician who says a cure for cancer will be long, expensive and may not work at all, and (b) a salesperson who says that several bottles of a secret formula "snake oil" will cure not only cancer but tuberculosis as well, some individuals will opt for "snake oil".Many "snake oil" remedies are highly laced with alcohol or narcotic drugs. Anyone who drinks them may get so drunk or stoned that they drown their pains in the rising tide of pleasant intoxication. Little wonder that "snake oil" is a popular cure-all for minor aches and hurts! But let there be no misunderstandings. A very few "home remedies" actually work. However, most remedies sold by quacks are not only useless, but often can be harmful as well.

The sentence "pain seems to be a chronic human condition" means pain seems to________.

A．be very serious

B．be very difficult

C．last for a long time

D．be always happening

读下面我国地形图，完成下列问题：

（1）我国地势特征___________________________________________________________。

（2）长江发源于  ______高原，注入  ______海，流经三级阶梯和季风区，有“水能宝库”和“黄金水道”之称。“九曲黄河万里沙，浪淘风波自天涯”，黄河含沙量的90%来自黄河的  ________高原。

（3）海南岛的主要耕地类型为  ___________。

（4）位于闽赣交界处的东北-西南走向的山脉是_____________________________。