1、单选题：
About the positive feedback control system, which one of the following is correct? （ ）
选项：
A:There is no positive feedback control system in the physical world.
B:I don’t know
C:There is positive feedback control system in the physical world.
答案: 【There is positive feedback control system in the physical world.】

2、多选题：
The representative figure in the history of classical control theory includes. （ ）
选项：
A:H. W. Bode
B:Harry Nyquist
C:James Clerk Maxwell
D:H. S. Black
答案: 【H. W. Bode;
Harry Nyquist;
James Clerk Maxwell;
H. S. Black】

3、多选题：
In the following utilities, the closed-loop systems include （ ）.
选项：
A:Washing machine
B:Air conditioner
C:Van elevator
D:Microwave oven
答案: 【Air conditioner;
Van elevator】

4、单选题：
The trend of control development is （ ）.
选项：
A:High autonomy, High flexibility
B:High autonomy, Low flexibility
C:Low autonomy, Low flexibility
D:Low autonomy, High flexibility
答案: 【High autonomy, High flexibility】

5、单选题：
A system with more than one input variable or more than one output variable is known by what name? （ ）
选项：
A:Multivariable control system
B:Closed-loop feedback system
C:Open-loop feedback system
D:Robust control system
答案: 【Multivariable control system】