Option A is incorrect because routes are designed for network traffic forwarding between networks, not for managing access to specific ports on a VM. Option B is incorrect as merely tagging a VM does not automatically implement the necessary firewall rules to control traffic. Option C is correct because it involves both tagging the VM and creating a specific firewall rule to allow incoming (ingress) traffic on UDP port 636, ensuring clients can access the LDAP server. Option D is incorrect since it focuses on outgoing (egress) traffic, which does not address the requirement for clients to access the server. For more information, refer to Google Cloud's documentation on firewalls, ingress and egress rules, and routes.