The problem appears to be a visual puzzle involving the addition of 3D cube shapes. Here's how to approach it:

1. You are given three elements, where the first two shapes are provided, and the third one is missing (denoted by "?"). The result of this sum is the complete cube shown at the right side of the equation.
2. The first shape (leftmost) consists of smaller cubes forming a more irregular structure. The second shape (middle) is nearly a cube but with a few cubes missing.
3. The goal is to identify which option (A, B, C, or D) completes the structure to form the final cube.

Solution:

• The final cube appears to be a perfect 3x3 cube, which has 27 small cubes in total.
• By visually adding the two given shapes (irregular and near-complete), we need to find which of the options (A, B, C, D) fills in the remaining space to form the full cube.

By examining the provided shapes and matching the remaining space with the options, Option D is the one that fills the missing cubes to complete the perfect 3x3 cube.

Conclusion:

The correct answer is D.

Let me know if you need further details or have any questions! Here are 5 related questions you can explore next:

1. How can spatial reasoning be enhanced through 3D puzzles?
2. What is the significance of 3D cube puzzles in cognitive ability tests?
3. How many total cubes are there in a perfect 3x3x3 cube?
4. How does visualizing shapes in three dimensions help in real-world problem-solving?
5. What are the most common strategies to solve 3D spatial puzzles quickly?

Tip: Practicing with puzzles that involve spatial awareness can improve your problem-solving skills and enhance memory functions.