“阿拉伯数字”在我们的学习、工作和生活中运用相当广泛。这一写法的出现大约在 [ ]
A．10世纪
B．12世纪
C．14世纪
D．16世纪
答案：B
The moment______John will never forget is______Mr．Smith gave him a lot of valuable advice on how to improve his writing．
A．that; that
B．that; when
C．when; that
D．when; when
同轴电缆内导体的半径为a，外导体的内半径为c，在a0应为（）。
A.
B.
C.
D.
