Which auth method is ideal for machine to machine authentication?

When Vault is sealed, which are the only two options available to a Vault administrator? (select two)

After creating a dynamic credential on a database, the DBA accidentally deletes the credentials on the database itself. When attempting to remove the lease, Vault returns an error stating that the credential cannot be found. What command can be run to coerce Vault to remove the secret?

What type of token does not have a TTL (time to live)?

An application is trying to use a secret in which the lease has expired. What can be done in order for the application to successfully request data from Vault?