Question: Describe how the validation is set up and configured in this reactive forms example:

1. The `FormControl` for `username` is getting configured to exclude three validators from the validators that it is allowed to use.
2. The `FormControl` for `username` is getting configured to allow three possible validators to be used: `required, maxLength`, and a custom one named `unique`. To enable these `validators`, a validator directive would need to be put on the form fields in th
3. Validation cannot be set up this way in reactive forms.
4. The `FormControl` for `username` is getting configured with three validators: the `required` and `minLength` validators that come from Angular, and a custom validator function named `unique` that checks for the value not equal to the string `admin`.

Answer: The correct answer of the above question is Option D:The `FormControl` for `username` is getting configured with three validators: the `required` and `minLength` validators that come from Angular, and a custom validator function named `unique` that checks for the value not equal to the string `admin`.