13-7. The geologist needs to know what rocks the drill has reached, so every so often a sample is obtained with a coring bit.


【讲解】the geologist中的the表示类别,指“地质学家这类人”。


every so often:时常。

13-8. It cuts a clean cylinder of rock, from which can be seen the strata the drill has been cutting through.


【讲解】can be seen the strata…through乃倒装结构,自然语序是the strata…through can be seen。因为主语过长,倒装可以避免头重脚轻。the drill has been cutting through是定语从句,修饰strata。

13-9. Once we get down to the oil, it usually flows to the surface because great pressure, either from gas or water, is pushing it.


【讲解】once we get down to the oil是时间状语从句,once是连接词。句中的两个it都指oil。either from gas or water乃非限制性定语,修饰pressure。

13-10. This pressure must be under control, and we control it by means of the mud which we circulate down the drill pipe.




circulate: 环行;环流;循环(to move around within a system, or to make something do this),

The earth circulates around the sun. 地球绕着太阳转。

Blood circulates through the body. 血液在体内循环。

13-11. We endeavour to avoid the old, romantic idea of a gusher, which wastes oil and gas.



13-12. We want it to stay down the hole until we can lead it off in a controlled manner.


【讲解】句中两个it都指oil。to stay down the hole作宾语补足语。