The correct answer is B and C. You must create firewall rules for health checks and reserve a static IP address for the load balancer before creating the internal HTTP(S) load balancer.
The other options are not correct because:
Option A is not a prerequisite task. You can choose a region when you create the load balancer, but you do not need to do it beforehand.
Option D is not a prerequisite task. You can determine the subnet mask for a proxy-only subnet when you create the subnet, but you do not need to do it beforehand.
Option E is not related to the internal HTTP(S) load balancer. Serverless VPC Access is a feature that allows you to connect your serverless applications to your VPC network, but it is not required for the load balancer.