What are the signs that indicate biological material has been fully cleaned and sanitized?

The presence of no visible residue or odors is a key indicator that biological material has been thoroughly cleaned and sanitized. When a surface is effectively cleaned, it should not only appear clear of contaminants but also lack any unpleasant smells that could indicate the presence of organic material or residues. Biological materials often carry odors, so their absence suggests successful sanitation.

Subsequent choices, while potentially relevant in different contexts, do not indicate that cleaning and sanitization have been adequately performed. The use of harsh chemicals may lead to the elimination of some biological contaminants, but it doesn't guarantee that all contaminants have been removed nor does it imply thorough cleaning. Similarly, the presence of cleaning agents alone does not confirm the effectiveness of cleaning; it's possible to have residues of cleaners without achieving proper sanitation. Verification by a client may confirm satisfaction with a job but does not inherently denote that the cleaning was done to the required standards. Therefore, the absence of visible residue or odors is the most definitive sign of proper cleaning and sanitization.