A:has opened; haven't gone
B:has been open; haven't been
C:has been open; haven't gone
D:has been opened; haven't been
如图,阳光通过窗口照到教室内,竖直窗框在地面上留下2.1m长的影子如图所示,已知窗框的影子DE到窗下墙脚的距离CE=3.9m,窗口底边离地面的距离BC=1.2m,试求窗口的高度.(即AB的值)
下列有关水资源的认识中,错误的是( )