有永久性顶盖的室外楼梯按( )计算建筑面积。
A．水平投影面积
B．水平投影面积的一半
C．不
D．建筑物自然层的水平投影面积的一半
参考答案：D
It was ________ he came back from Africa that year ________ he met the girl he would like to marry.[ ]
A. when; then
B. not; until
C. not until; that
D. only; when
生态系统是一个动态系统，要经过由简单到______的发育过程。
