Interpretation and analysis: the first person has four choices, the second person has two choices, and the third person and the fourth person have only one choice. Answer accordingly.

Solution: The first person has four choices, the second person has two choices, and the third person and the fourth person have only one choice. Therefore, a * * * has: 4×2× 1× 1=8 (species).

A: There are eight ways to stop.

Comments: This question can also be answered as follows: Let Zhengzhou code be 1, Xiao Li code be 2, Dawn code be 3 and Xiao Fang code be 4. Then there are eight ways to stop * * *, as follows:

1234, 1432,2 134,243 1,32 14,34 12,4 123,432 1。

Addition principle sum classification counting method.

1, addition principle: There are n ways to accomplish something. The first way has m 1 different ways, the second way has m2 different ways, and the nth way has mn different ways, so there are N=m 1+m2+m3+mn ways to complete it.

2. The method of the first method belongs to the set A 1, the method of the second method belongs to the set A2, and the method of the nth method belongs to the set An, so the method to accomplish it belongs to the set A 1UA2U, UAn.