WD drive will not recgnize my PC c: drive for backing up

When I try to set up a back-up plan using my c:drive, the WD drive only recognizes the cloud. What might I be doing wrong? I passed all the tests in setting up the WD drive.

What type of backup are you trying to do?

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Have you read the User Manual for your generation of My Cloud?

https://support.wdc.com/product.aspx?ID=904&lang=en