I wrote AccountsSelector class but I still can't pass the challange.
Where could I be wrong?
Code:

public with sharing class AccountsSelector extends fflib_SObjectSelector{
    
   public List<Schema.SObjectField> getSObjectFieldList() {
        return new List<Schema.SObjectField> {
            Account.Id,
            Account.Description,
            Account.Name,
            Account.AnnualRevenue };
    }
    
    List<Account> selectById(Set<ID> idSet) {
      return (List<Account>) selectSObjectsById(idSet);
    }

     public Schema.SObjectType getSObjectType() {
        return Account.sObjectType;
    }

}