Final answer:
From Powershell, use the Set-PasswordPolicy cmdlet with the -Tenant parameter to implement a strong password policy across an entire tenant.
Step-by-step explanation:
From Powershell, you can implement a strong password policy across an entire tenant using the cmdlet Set-PasswordPolicy with the -Tenant parameter. The correct option is d) Set-PasswordPolicy -Tenant <tenant_name> -Strength Strong.
For example, if the tenant name is 'example', the command would be Set-PasswordPolicy -Tenant example -Strength Strong. This will set a strong password policy for the specified tenant.