Geometric block shapes and their 2D projection views arranged in a 4x6 grid.

Problem Analysis:

The task involves matching 3D geometric shapes (labeled A–Y) with their corresponding top-down projections (labeled 13–24). The goal is to identify which projection corresponds to each 3D shape.

Solution Approach:

1. Understand the 3D Shapes: Each 3D shape (A–Y) has a unique structure, including hollow sections, protrusions, and steps.
2. Analyze the Projections: The top-down projections (13–24) show the outline of the shapes as seen from directly above. These projections ignore height and only show the horizontal layout.
3. Match Shapes to Projections: For each 3D shape, visualize how it would look when viewed from directly above and match it to one of the projections.

Step-by-Step Matching:

#### Shape A:
- Description: A cube with a square hole in the center.
- Projection: Matches 13 because it shows a square with a smaller square hole in the center.

#### Shape B:
- Description: A cube with a rectangular cutout on one side.
- Projection: Matches 14 because it shows a square with a rectangular indentation on one side.

#### Shape C:
- Description: A cube with a triangular cutout on one side.
- Projection: Matches 15 because it shows a square with a triangular indentation on one side.

#### Shape D:
- Description: A cube with a diagonal cutout.
- Projection: Matches 16 because it shows a square with a diagonal line indicating the cutout.

#### Shape E:
- Description: A cube with a protrusion on one side.
- Projection: Matches 17 because it shows a square with an additional rectangle extending from one side.

#### Shape F:
- Description: A cube with a protrusion on two adjacent sides.
- Projection: Matches 18 because it shows a square with two rectangles extending from adjacent sides.

#### Shape G:
- Description: A cube with a protrusion on three adjacent sides.
- Projection: Matches 19 because it shows a square with three rectangles extending from adjacent sides.

#### Shape H:
- Description: A cube with a protrusion on all four sides.
- Projection: Matches 20 because it shows a square with four rectangles extending from all sides.

#### Shape I:
- Description: A cube with a step-like structure on one side.
- Projection: Matches 21 because it shows a square with a smaller square inside, indicating a step.

#### Shape J:
- Description: A cube with a step-like structure on two adjacent sides.
- Projection: Matches 22 because it shows a square with two smaller squares inside, indicating steps on two sides.

#### Shape K:
- Description: A cube with a step-like structure on three adjacent sides.
- Projection: Matches 23 because it shows a square with three smaller squares inside, indicating steps on three sides.

#### Shape L:
- Description: A cube with a step-like structure on all four sides.
- Projection: Matches 24 because it shows a square with four smaller squares inside, indicating steps on all sides.

Final Matchings:

- A → 13
- B → 14
- C → 15
- D → 16
- E → 17
- F → 18
- G → 19
- H → 20
- I → 21
- J → 22
- K → 23
- L → 24

Conclusion:

By carefully analyzing the 3D structures and their corresponding top-down projections, we can confidently match each shape to its projection. The final answer is:

\[
\boxed{A \rightarrow 13, B \rightarrow 14, C \rightarrow 15, D \rightarrow 16, E \rightarrow 17, F \rightarrow 18, G \rightarrow 19, H \rightarrow 20, I \rightarrow 21, J \rightarrow 22, K \rightarrow 23, L \rightarrow 24}
\]