Which of the following are valid choices for the LDAP database backend? (Choose THREE correct answers.)

"file" is not a standard, named OpenLDAP database backend; typically, backends like `bdb` or `hdb` store data in files.

The `config` backend (`cn=config`) is a dynamic, in-memory database used by OpenLDAP 2.4 and later to manage the server's configuration, allowing it to be changed without restarting the daemon.

The `passwd` backend allows OpenLDAP to authenticate users against the local system's password database (e.g., `/etc/passwd` or `/etc/shadow`), which can be useful for integration or simple deployments.

`lbdm` is not a recognized standard backend for OpenLDAP. Popular traditional backends include `bdb` (Berkeley DB) and `hdb` (Hierarchical DB), and newer ones like `lmdb`.

The `shell` backend provides a mechanism to interface OpenLDAP with external programs or scripts, allowing them to handle LDAP operations, offering flexibility for custom integrations or specialized data storage.