A company salesman wants to visit the four cities

a, b,

c, d wherein his company has stores. If he plans to visit each city once, give a suitable sample space to describe the order in which he visits the cities. Then identify, by an appropriate listing of its elements, each of the following events:

A1: the salesman visits first city b;

A2: the salesman visits city b first and after that visits city d;

A3: the salesman visits city a before he visits city d;

A4: the salesman visits the cities

a, b, c successively.