In Microsoft Azure, a route table is used to control network traffic flow. A route table

contains a set of rules, called routes, that specify how packets should be directed. A route

table can be associated with one or more subnets within a virtual network. It cannot be

associated directly with a virtual network (VNet) or a network interface (NIC). Therefore,

among the given options, the route table RT1 can only be associated with Subnet1.

References:

Microsoft Learn | Virtual network traffic routing: "You can create custom route tables that

control where packets are routed for each subnet. ... You can associate a route table to

zero or more subnets."

URL: https://learn.microsoft.com/en-us/azure/virtual-network/virtual-networks-udroverview#association-of-a-route-table-to-a-subnet

Microsoft Learn | Create, change, or delete a route table: "A route table can be associated

to zero or more subnets. A route table can't be associated to a virtual network."

URL: https://learn.microsoft.com/en-us/azure/virtual-network/manage-routetable#associate-a-route-table-to-a-subnet

Microsoft Learn | Virtual network traffic routing: "You can create custom route tables that

control where packets are routed for each subnet. ... You can associate a route table to

zero or more subnets."

URL: https://learn.microsoft.com/en-us/azure/virtual-network/virtual-networks-udroverview#association-of-a-route-table-to-a-subnet

Microsoft Learn | Create, change, or delete a route table: "A route table can be associated

to zero or more subnets. A route table can't be associated to a virtual network."

URL: https://learn.microsoft.com/en-us/azure/virtual-network/manage-routetable#associate-a-route-table-to-a-subnet