We must try to use every means to protect the earth
其实 We must try every means to protect the earth 这样说是最简单的,但如果一定要把横线填满,就用上面的方法：try to do sth.有尽力做某事的意思,every means也可写成each means
尽管我也不能保证答案一定对 但还是希望能够帮助到你