To stop a problem you have to understand its underlying causes.

要想杜绝问题的发生，必须弄清它的深层原因。

I think that the underlying problem is education, unemployment and bad housing.

我认为深层的问题在于教育、失业和糟糕的住房条件。

...hills with the hard underlying rock poking through the turf.

坚硬的下层岩石穿过草皮凸出来的山丘

Cars were covered with clear-coat finish at the factory to protect the underlying paint from fading.

工厂给汽车上了透明罩漆，以防底漆褪色。