There aren't _ food on the table.[ ]
A. some
B. a
C. an
D. any
答案：D
Although he talked half an hour, he couldn't give us a good ________ of the reason why he did it.
A．idea
B．explanation
C．sense
D．understanding
（）可以做为工件的工序基准。
A、只有实际表面
B、只有几何中心
C、只有对称面或对称线
D、A、B和C
