The following release pipeline has been defined in Azure DevOps. 

The Artifacts section has been defined to pick up the artifacts from a build pipeline defined in Azure DevOps. 
You need to ensure that the release pipeline deploys the source to an Azure Web App. Which of the following must you add to the pipeline?

Answer options:

A.A gate
B.A task
C.A variable
D.A release

Answer – B 
You need to add a task to the pipeline as shown below. 

Since this is clear from the implementation, all other options are incorrect. 
For more information on deploying to Azure Web Apps, please visit the following URL- 

https://docs.microsoft.com/en-us/azure/devops/pipelines/apps/cd/deploy-webdeploy-webapps?view=azure-devops