Question

be covered by/with有什么区别？怎么用

Answer 1

be covered by意为“被……所覆盖”,是被动语态,“为……所覆盖”还可用be covered with来表示,但这不是被动语态,而是系表结构,注重于事物的状态,可译为“到处都是”.例：The mountain was covered with snow all the year round.这座山一年到头都被雪覆盖着.
It must have rained last night,for the ground is covered with water.昨晚一定下过雨,因为底上到处都是水
另外be covered by ...:还有“由...承担/负担/支付;被...掩护/报道/监视/控制等等,表示抽象的概念,后面接人,机构,或者组织.”的意思.
These expenses are covered by the state