You need to regenerate the service proxies to include task-based asynchronous method signatures.
Which command should you use?
A. aspnet_regiis.exe /t:code http://localhost:62965/UploadCallbackService.svc
B. svcutil.exe /t:code http://localhost:62965/UploadCallbackService.svc
C. aspnet_compiler.exe /t:code http://localhost:62965/UploadCallbackService.svc
D. aspnet_regiis.exe /t:code http://localhost:62965/UploadService.svc
E. svcutil.exe /t:code http://localhost:62965/UploadService.svc