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

对同一台四冲程非增压柴油机，一般地说（）。

A．排气阀面积大于进气阀

B．排气阀面积小于进气阀

C．排气阀寿命大于进气阀

D．排气阀无阀壳而进气阀有阀壳