(66) method is the use of a data processing system to represent selected behavioral (67) of a physical or abstract system. For example, the representation of air streams around airfoils at various velocities, temperatures, and air pressures with such a system.

Emulation method is slightly different, it uses a data processing system to imitate another data processing system, so that the imitating system accepts the same data, executes the same programs, and achieves the same (68) as the imitated system. Emulation is usually achieved (69) hardware or firmware. In a network, for example, microcomputers might emulate terminals (70) communicate with mainframe.

（70）处填（）。

A．in order to

B．for

C．therefore

D．to this end

模拟信号u（t）的波形图如图所示，它的时间描述形式是：().

A．u(t)=2(1-e^-10t)·(t)

B．u(t)=2(1-e^-0.1t)·1(t)

C．u(t)=[2(1-e^-10t)-2·1(t)

D．u(t)=2(1-e^-10t)·1(t)-2·1(t-2)