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If your disk is more complicated and cannot be operated by the above steps, in such situations, you can use third party tools like freeware Partition Resizer Free to extend the partition without much trouble. Video - how to shrink volume and then extend volume in disk management In fact, enabling extend volume in disk management can be done by deleting volume or shrinking volume. Even sometimes you cannot shrink your drives as it reaches the shrink limit.
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It is not possible to move the unallocated space that you have just created to the right adjacent side of C drive from disk management tool and thus you cannot extend your C drive. But do you really want to delete your D partition? You will loose your data from D drive.
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