去掉原来的助动词be，把主语变成宾语即可。

例如: A great many young trees have been planted around our school over the last two years.过去的两年在我们学校周围栽种很多小树。变成主动语态：We have planted a great many young trees around our school over the last two years.过去的两年在我们学校周围我们栽种了很多小树。