Which of the following is critical for protecting surfaces not intended to be painted?

Using painter's tape and drop cloths is essential for protecting surfaces not intended to be painted. Painter's tape allows for clean lines by preventing paint from bleeding onto adjacent surfaces, while drop cloths protect floors and furniture from spills and splatters during the painting process. These protective measures ensure that only the intended areas receive paint, helping to maintain a professional finish and avoid costly touch-ups.

The other options serve different purposes in the painting process. Sanding surfaces is vital for ensuring proper adhesion of the paint, but it does not protect unintended surfaces. Painting in daylight can improve visibility, but it does not directly aid in the protection of other surfaces. Similarly, using low-VOC paints relates to environmental and health considerations rather than surface protection. Thus, the use of painter's tape and drop cloths is the most critical measure to safeguard areas not intended for painting.