工事的英文：
stuctures used to protect military troops
fortifications

参考例句：

Fortify a city
筑工事以巩固城防

chemical,biological and radiological protectiveinstallations in shelter
工事防化设施

The Great Wall is difficult to slight.
长城是难以拆毁的一道工事。

A narrow entrance into the outwork of a fortification.
狭窄入口要塞的外围工事的狭窄入口

The regiment secured its position while awaiting the enemy attack
该团在等待放人进攻之时加强了阵地工事。

A minor fortification constructed beyond a main defensive position or fortification.
简易外围工事在主要防御位置或防御工事之外构筑的小防御工事

People have been mobilised to build defences and drain flooded land as heavy rains continue to fall.
大雨还在继续下，人们已经被动员起来修筑防洪工事，为遭淹田地排水。

Raised earthworks inside the city walls could greatly reduce the effects of artillery bombardment
城墙以内突起的土木工事可以大大减少大炮轰击的效果。

used是什么意思：
adj. 用过的，旧的；习惯于…的

It is used as a reflexive.
它被作为反身代词使用。

That was a balk to us.
那对我们是个挫折。

They help us to be maximal encouraging to us.
他们来帮助我们对我们是个极大的鼓舞。

protect是什么意思：
v. 保护，保卫

A protective overlay, as for a mattress or furniture.
护套保护性的饰布，如坐垫或家具。

a protective case for a knife or sword.
刀或剑上的保护性外壳。

invoke the protection of...
祈求…的庇护