1. His philosophical work is notoriously impenetrable. 他的哲学著作是出了名地令人费解。
2. Their jargon is impenetrable to an outsider. 他们的行话外人听不懂。
3. No system is impenetrable, and none can promise to eliminate the worst case completely. 没有哪个系统是不可攻破的，也没有哪个系统能够保证完全杜绝最坏的情况发生。
4. The familiar chestnut, oak, and elm grew taller here, and the forest rimming the clearing appeared thick and impenetrable. 熟悉的栗树、橡树和榆树在这里长高了，空地周围的森林显得茂密而密不透风。
5. On the other side of the rise, an endless impenetrable thicket of poison oak and coyote brush hides quail and other members of its guild. 在另一边，则生活着无边浓密的毒橡林和藏着鹌鹑的郊狼灌木丛以及其他成员。
