The problem requires identifying three potential squares to complete the net of a cube. A valid net of a cube must have six faces that can fold into a 3D cube.

Observations:

The provided net currently has five squares shaded. The sixth square can be added in such a way that the final net forms a valid cube. Below are the potential squares where the extra face can be added:

1. Above the top-center square: Adding a square directly above the middle square will result in a valid cube net.
2. To the left of the top-center square: Adding a square to the left of the middle square creates another valid cube net.
3. To the right of the top-center square: Adding a square to the right of the middle square also completes the cube net.

These three options represent all possible valid additions to the net.

Solution:

Shade the three possible squares as follows:

1. The square above the top-center square.
2. The square to the left of the top-center square.
3. The square to the right of the top-center square.

Would you like a diagram or further clarification? Here are some follow-up questions you might consider:

1. Why are other squares invalid for completing the net of a cube?
2. How can you verify that a net folds into a valid cube?
3. Can other geometric shapes besides cubes have nets like this?
4. What are common properties of all cube nets?
5. How many total unique nets can a cube have?

Tip: Always count the faces to ensure a proper net for any 3D shape!