The correct answer is B because the firewall rule must be associated with the instance for the rule to apply. This association is achieved by applying the network tag 'dev-ssh' to the instance. Network tags are text attributes that can be added to Compute Engine VM instances, allowing firewall rules and routes to be applied to specific instances. These tags can be added at any time without stopping the instance.

• Option A is incorrect because firewall rules associated through network tags take effect immediately and do not require a refresh.
• Option C is incorrect because firewall rules do not need to be reloaded; they are applied immediately.
• Option D is incorrect because the issue lies with the target tags, not the source tags, which dictate the instances the rules apply to.