改错。

下面短文中有10处语言错误。请在有错误的地方增加、删除或修改某个单词。

增加：在缺词处加一个漏字符号（∧），并在其下面写上该加的词。

删除：把多余的词用斜线（＼）划掉。、

修改：在错的词下划一横线，并在该词下面写上修改后的词。

     A few years ago, some tourists pay no attention to environmental protection. They threw waste things

about, like plastic bags, fruit skins and waste papers. Sometimes they broke trees, picked up flowers and killed birds; some even made fires in the woods to cook for picnics. What dangerous it was! Fortunate,

great changes have been taken place here. All the tourists have got  used to put their rubbish into dustbins. But they are making great efforts to protect birds and plants as well .They bring our own meals prevent

any accidental fire. All these should be appreciated

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顺序阀不能在系统中用作（）。

A.液控开关

B.平衡阀

C.背压阀

D.调压阀