Solution:
There is 2 possibility for the first letter from the left.
Then there are 2 possibilities for the second letter. Then and so on till the 5-th letter.
In this way, you will get
[tex]2^{5\text{ }}=32[/tex]
Each is unique, and each is achievable in this way.
There are no other arrangements. So that, we can conclude that the correct answer is:
[tex]32[/tex]
