defend: denotes warding off or repelling actual or threatened attacks: a large army needed to ~ the country.


protect: implies the use of something as a bar to the admission or impact of what may attack, injure, or destroy: ~ one's eyes from the sun with dark glasses.          bar作名词表示金属条或棒，作动词表示阻止排除禁止=debar=prevent，如amnesty workers have been barred from Sri Lanka since 1982从1982年起，大赦国际工作人员就被禁止进入斯里兰卡


shield: suggests the intenvention of a cover or barrier against imminent danger or actual attack: tried to ~ her child from the real world.       本义是盾牌           (barrier 1、阻隔物障碍物壁垒，如篱笆围墙something such as a fence or wall that prevents people from moving to another area，如the barriers kept the crowd back障碍物拦住了人群，如trade barriers贸易壁垒  2、分界线屏障，如山川something that keeps things separate，如 barrier between reality and fantasy in his mind现实与幻想之间的界线，如the Yangtze river is a natural barrier to the north-east长江是东北方向的一道天然屏障)


guard: implies protecting with vigilance and force against expected danger: all White House entrances are well ~ed.


safeguard: implies the taking of precautionary protective measures against merely potential dangers: individual rights must be ~ed whatever the cost.         常用于抽象或比喻义，如保障工作，捍卫健康、主权一般用这个词，如本例保障或捍卫权利   potential和上边的expected都表示很可能发生的，没有译出


defend防御防卫: 指阻挡或击退攻击，protect保护: 指使用某物阻隔使免受攻击或伤害，shield屏障屏蔽: 指使用盾牌或屏障保护，guard守卫: 指警惕有力的保护，safeguard保障捍卫: 强调预先防范


记忆方法： 1） 首字母DPSGS联想为GPS Defence SystemGPS防御系统<==保护
         
          2）保护的意思是维持安全免于危险攻击mean to keep secure from danger or against attack.