A route table RT1 is created in the East US region. Given the resources in the subscription, which resource(s) can RT1 be associated with?

Route tables in Azure are always associated with subnets, not virtual networks (VNets) directly or network interface cards (NICs). When a route table is associated with a subnet, all traffic leaving any virtual machine (VM) within that subnet will use the rules defined in the route table. While a VNet contains subnets, the routing is applied at the subnet level for granular control. NICs are components of VMs and inherit their routing behavior from the subnet they are connected to. Therefore, RT1 can only be associated with Subnet1.