1、站岗
...guard dog 看门狗，警卫狗...keep guard 站岗rear guard 后卫部队；殿后...
2、守卫
时态：过去进行时 keep guard 守卫 to their surprise 使他们吃惊的是 ..
3、守望
...body guard 保镖keep guard 守望，警戒They kept a close guard over the thieves. 他们对小偷们严加看管。 ...
4、警戒
... the Customs House 海关 keep guard 警戒、守卫 precious 珍贵的 ...