How would you migrate the source code from Team Foundation Server to Azure DevOps?

Answer options:

A.Migrate the server onto Azure DevOps.
B.Import the server onto Azure DevOps.
C.Clone repository into Azure DevOps.
D.Import repository into Azure DevOps.

Answer - D 
You can do an import of the registry. An example of this is given in the Microsoft documentation. 

Since this is clearly given in the documentation, all other options are incorrect. 
For more information on importing from Team Foundation Version Control, please visit the below URL- 

https://docs.microsoft.com/en-us/azure/devops/repos/git/import-from-tfvc?view=azure-devops