每课一句：新概念第2册第88课
【往期回顾】
今天我们接着来看第88课的“每课一句”。
一、课文原文
Lesson 88 Trapped in a mine
Six men have been trapped in a mine for seventeen hours. If they are not brought to the surface soon they may lose their lives. However, rescue operations are proving difficult. If explosives are used, vibrations will cause the roof of the mine to collapse. Rescue workers are therefore drilling a hole on the north side of the mine. They intend to bring the men up in a special capsule. If there had not been a hard layer of rock beneath the soil, they would have completed the job in a few hours. As it is, they have been drilling for sixteen hours and they still have a long way to go. Meanwhile, a microphone, which was lowered into the mine two hours ago, has enabled the men to keep in touch with the closest relatives. Though they are running out of food and drink, the men are cheerful and confident that they will get out soon. They have been told that rescue operations are progressing smoothly. If they knew how difficult it was to drill through the hard rock, they would lose heart.
——选自《新概念英语》第二册，外语教学与研究出版社，1997年10月第1版
二、每课一句
If there had not been a hard layer of rock beneath the soil, they would have completed the job in a few hours.
本课侧重复习if引导的条件句，包括真实条件句和非真实条件句（即虚拟条件句），而上面这句话中if引导的就是非真实条件句。
这句话针对的是过去发生的事情的虚拟，所以其用法为：
if...had done..., ...would have done...
即：
if所在的从句谓语动词采用过去完成时，而其主句谓语动词则采用“情态动词+have done”的用法
此外，本课课文中的最后一句也采用了非真实条件句：
If they knew how difficult it was to drill through the hard rock, they would lose heart.
只是，本句话针对的是现在时间的虚拟，其用法为：
if...did..., ...would do...
即：
if所在的从句谓语动词采用一般过去时，而其主句谓语动词则采用“情态动词+do”的用法
三、更多拓展
However, rescue operations are proving difficult.
注意这句话中的prove不是用作系动词，而是用作了行为动词，所以可以采用现在进行时，来表示营行动正在被证实是有困难的。
当prove用作系动词时，其后常接to be，然后再接形容词或名词，如：
None of the rumours has ever been proved to be true.
这些谣言没有一个被证明是真的。
此时的prove就相当于turn out。