"Account Operator" group users are npt able to reset NT ac..

Below is the setup

1) In out Current setup, Domain Admin Group member users can reset the
password for all NT users domain account. Due to this our domain and servers
are not secure with end users.
2) Our question is why users who are the member of "Account Operator" are
not able to reset the password for any NT users domain account? We want
"Account Operator" users should able to reset the password for all NT user
account.
3)for testing we have created one test user account and made the member of
below groups i.e. domain Users group, Account Operator Group.

Still the test user is not able to reset the password for other NT user
account within a same domain.

4) Need your assistance and help to resolve password reset issue.