To 'sully' something means to:

To 'sully' something means to damage its purity or integrity, resulting in a tarnished or compromised state. The term is often used in contexts where something once clean, pristine, or revered has been marred or spoiled. The essence of the word captures the notion of an undesirable change, usually associated with moral or ethical standards, but it can also apply to physical items, experiences, or reputations.

In contrast, the other options suggest improvements or positive contributions—enhancing quality, promoting integrity, or restoring value—which are inconsistent with the meaning of 'sully.' These choices imply actions that uplift or rectify, rather than the degradation that 'sully' inherently conveys. Thus, the selection representing damage to purity accurately reflects the definition and usage of the term 'sully.'