In the 1950s in the USA, most families had just one phone at home, and wireless phones _______ yet.
A:haven't invented
B:haven't been invented
C:hadn't invented
D:hadn't been invented
糖尿病是一种激素分泌异常造成的非传染性疾病,我国患糖尿病的人数居世界首位.糖尿病发病的主要原因是( )
有人用“观念转变,黄金万两”来解释戊戌变法对中国社会的影响。下列哪项最符合这种解释( )
好朋友要去外地了,临别时你想告诉他你会想他的,你可以说: