A team wants to make use of Azure Pipelines for the continuous deployment of applications. The applications need to be deployed onto a set of Azure virtual machines. 
Which of the following makes it easier to target the application release on a set of virtual machines?

Answer options:

A.Agent pool
B.Deployment groups
C.ARM agents
D.Resource groups

Answer – B 
You can create a deployment group and install agents on each of the servers as part of the deployment group. 
This is also mentioned in the Microsoft documentation. 

Since this is clearly mentioned in the Microsoft documentation, all other options are incorrect 
For more information on using deployment groups, please refer to the following link 

https://docs.microsoft.com/en-us/azure/devops/pipelines/release/deployment-groups/?view=azure-devops