以下（）不属于短波自适应通信技术的。
A.实时信道估值技术
B.实时选频
C.自动建立线路
D.智能天线。
参考答案：D
Not until they left school ________ how much their teachers loved them and helped them. [ ]
A. they realized
B. had they realized
C. they would realize
D. did they realize
北京师范大学学制研究小组于1981年在其附属中小学开始进行的学制实验是（）
A.六三制
B.双轨制
C.分支型
D.五四制
