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#11
Looking at your Disk Mgmt screenshot, I don't see any reason D: cannot be deleted in Disk Mgmt and added to your C: drive. It doesn't appear to be a Recovery Partition, which is to the left of C:
The best recovery method is to save a Win7 Backup Image externally along with your backed up files.
Once deleted, here's how to extend your C: drive: Partition or Volume - Extend
If you want us to take a look at your actual recovery partition, then post back a screenshot of its contents after unhiding files in Control Panel>Folder Options>View.