A company has a Virtual Network and wants to implement the following requirements To create 2 subnets and 2 VM’s in each subnet
To create a user defined route to enable the 2 subnet resources to communicate
Can a user defined route be created without creating Subnet?

Answer options:

A.UDR cannot be created without creating Subnet
B.UDR can be created without creating Subnet
C.At-least one UDR is required to create a Subnet
D.There is no relation between Route and Subnet

Answer: B 
Option A is incorrect because there is no mandatory validation to have a subnet while creating an UDR 
Option B is CORRECT because UDR can be created prior to creation of the Subnet. But it would be effective only once the route is associated with Subnet. Please refer to the reference url 
Option C is incorrect because though UDR is required to associate with Subnet, it is not required during creation 
Option D is incorrect because UDR is relevant when resources of the subnets communicate with each other 
Reference:

https://docs.microsoft.com/en-us/azure/virtual-network/virtual-networks-udr-overview