If cell "X" is blank leave cell "Y" blank, If cell "X" is true then allow list in cell "Y

Hiya, I'm new to Excel and I have already thought of something that I would like for it to do that is way over my head. I would greatly appreciate it if someone could provide some guidance + details on how to do it. Thanks in advance.

I need to allow a user to see a drop-down list (with options listed below) only when the previous cell has the word "Yes" which was also selected from a drop down. If the previous cell is blank then the current cell must be left blank and non-editable.

Drop down list:
-Not Started
-Pending
-Approved
-Not Approved

For example, cell C1 can only have the option to select "Yes". If C1 has "Yes" then I want the user to be able to select from a drop down list in D1. If C1 is blank then D1 is blank. NOTE: I want to limit the user to only being able to select from the options provided in the drop-down menu (I don't want C1 and D1 to be editable by the user)

Hope this is possible. Attached is the Test sheet. Test.xlsm