An analog signal’s characteristic quantity representing data may 66) . at any instant, any value within a continuous (67) . For example, an analog signal may follow continuously the values of another physical quantity representing data.

A discrete signal is composed of (68) elements in time, each element having one or more characteristic quantities which can represent data. Examples of characteristic quantities are amplitude, waveform, (69) , and position in time. A digital signal is a special case of discrete signals, in which data are represented by a (70) number of well-defined discrete values that one of its characteristic quantities may take in time.

（67）处填（）。

A．interval

B．region

C．range

D．compartment

下列选项不能删除换灯片的是（）

A.在幻灯片视图下，单击"编辑"→"删除幻灯片"，删除当前幻灯片

B.在幻灯片浏览视图下，选定要删除的幻灯片，按Del键

C.在大纲视图下，选定要删除的幻灯片，按Del键

D.在幻灯片视图下，单击"编辑"→"剪切"，删除当前幻灯片