Your company has an Azure DevOps project named tests. The project contains pipelines defined in Azure Pipelines that pick up code from GitHub repositories. You have to ensure that developers are able to receive Microsoft Teams notifications when there are failures in the pipeline. 
You have to complete the below command for this purpose. 

Which of the following needs to go into Slot 1?

Answer options:

A.feedback
B.signin
C.subscribe
D.subscriptions

Answer – C 
To ensure that you can subscribe to the pipeline, you have to issue the following command @azure pipelines subscribe [pipeline url] 
Options A, B and D are incorrect because the right way to subscribe is to use the azure pipelines subscribe command. 
For more information on the integration of Azure DevOps pipelines with Slack, you can refer to the below link- 

https://docs.microsoft.com/en-us/azure/devops/pipelines/integrations/microsoft-teams?view=azure-devops