What precaution must be taken regarding wine glasses?

The correct answer emphasizes the importance of perfect cleanliness when it comes to wine glasses. Clean glasses are crucial because any residue, dust, or previous wine residues can significantly affect the wine's taste and aroma. A clean glass ensures that the wine can express its full character and that the drinker can appreciate all the nuances of flavor and aroma. In professional settings, serving wine in clean glasses is part of providing a high-quality experience.

While colorful and decorative glasses (the first choice) may be visually appealing, they do not contribute positively to the tasting experience and could even distract from it. The third choice, regarding the size and weight of the glasses, does not impact their function; wine can be enjoyed from various styles of glasses depending on personal preference. Lastly, crystal glasses, while often associated with fine wine service, are not a strict requirement for enjoying or serving wine, and other materials can also do an effective job if they are clean.