The correct answer is option 'B': behind a screen.

Explanation:

Behind a screen, the masterpiece is hidden by the Master for the Emperor to see. Let's explore the reasons why this hiding place is the most suitable and logical choice.

1. Preservation:
The Master would have chosen to hide the masterpiece behind a screen to ensure its preservation. Screens provide protection against dust, sunlight, and other environmental factors that could potentially damage or fade the artwork. By hiding it behind a screen, the Master ensures that the piece remains in the best condition possible.

2. Concealment:
Hiding the masterpiece behind a screen offers a level of concealment. Screens are designed to act as barriers and partitions, often used to separate spaces or provide privacy. Placing the artwork behind a screen would make it less visible to those who are not intended to see it, thus increasing its security and reducing the risk of theft or unauthorized viewing.

3. Aesthetic Appeal:
Screens themselves are often considered works of art in many cultures. They are crafted with intricate designs and patterns, showcasing the artistic skills of the creator. By hiding the masterpiece behind a screen, the Master adds an additional layer of artistic beauty to the overall presentation. It creates an element of surprise and intrigue when the screen is moved aside to reveal the hidden artwork.

4. Cultural Significance:
In some cultures, screens hold significant cultural value. They are used as decorative pieces and are associated with wealth, status, and taste. By choosing to hide the masterpiece behind a screen, the Master acknowledges and respects the cultural significance of screens, elevating the status of the artwork and emphasizing its importance.

In conclusion, the Master chose to hide the masterpiece behind a screen to preserve its condition, provide concealment, enhance its aesthetic appeal, and respect the cultural significance of screens. This hiding place ensures that the artwork remains protected and adds an element of surprise and beauty when revealed to the Emperor.