I once lived in Arizona near fort Huachuca, an Army installation. Our street consisted mainly of mobile homes with small yards, but grass was difficult to grow in that climate, especially with the many children and dogs romping through（不费力地完成） the neighborhood. One lawn stood out, however. It was green and lush（丰富的，青葱的） with neat rows of flowers. I was puzzled how the owner managed to do it until I noticed a sign in the yard. It read: "Danger-Minefield（雷区） ."