Sequential circuit is a common logic device whose output values, at a given instant, depend upon its input values and the internal state at that instant, and whose internal state depends upon the (66) preceding input values and the preceding internal state. A sequential circuit can assume a finite number of internal states and may therefore be regarded, from an abstract (67) , as a finite (68) .
Combinational circuit is another logic device whose output values, at any given instant, depend upon the input values at that instant. A combinational circuit is a (69) of a sequential circuit whose internal state is not taken (70) .
（70）处填（）。
A．calculation
B．in account
C．audit
D．attention
参考答案：B
解析：
参考译文
时序电路是一种常见的逻辑器件，在给定时刻，其输出值取决于它在该时刻的各输入值和内部状态，而其内部状态又取决于紧接的前面各输入值和内部状态。时序电路能取有限个内部状态，因此，从抽象的角度可看成是一种有限自动机。
组合电路则是另一种逻辑器件，在任意时刻，其输出值都取决于该时刻的各输入值。组合电路是时序电路在不考虑其内部状态时的一种特例。