In 1620,about half the USA was covered by forests.此句子对吗?

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In 1620,about half the USA was covered by forests.此句子对吗?
将by换成with行吗?我看到别处有用with的.可是be covered with 与be covered by不能通用,有点晕.

我认为这个句子没错,在这里 by也可以换成with.当然be covered with 与be covered by不能通用,be covered by ...: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.eg.These expenses are covered by the state.(这些费用都由国家负担.)
All road out of town has been covered by the police .(所有出城的道路都被警察监视.)
be covered with\by ...:被...覆盖,表示具体的覆盖.如被雪/草地/布/被子/盖子/罩子等东西盖住.eg.
The furniture was covered by a lot of dust.(家具上满是灰尘.)
be covered with moss(长满绿苔)
be covered with snow all the year round(终年积雪）
再问：可是森林并不是人，机构或者组织，为什么用的是.........by呢？麻烦详细些。谢了。
再答： be covered with与 be covered by 这两个词语都有“由。。。覆盖”之意,，介词with用于主动或被动语态均可，指“用。。。覆盖/掩盖”，表状态。介词by用于被动语态，引出动作的逻辑主语，表动作。尽管森林并不是人，但它是动作cover的逻辑主语，所以用by。如果把by换成with，则是强调状态了。

In 1620,about half the USA was covered by forests.此句子对吗? 英语翻译In 1620，about half the USA was covered by forests.Today 英语翻译In 1620,about half the USA was covered by forests． Today In 1620,about half the U.S.A.was covered by forests. the Great Wall in Chian will be covered by forests ( ). In 1850,about a third of U.S.A___(be) covered by forests. The Great Green Wall in China will be covered by forests ( ） △In1850,about a third of U.S.A.( )covered by forests.A.were In 1620,about half of the USA___covered by forest A:are B:is In 1620,about half the USA__forest. 下面这个句子是什么,The girl was cring,her face covered by her hand.he We covered the distance in half an hour 为什么用covered