You are given three grids, where each of them is 5 by 5 in size.
Grids have empty cells marked with "▢" and filled cells marked with "X".
Your task is to generate a referring expression that best describes the target grid while distinguishing it from the two other distractor grids.
The first grid is the target grid, and the following two grids are the distractors.

Target grid:

X X X X ▢
▢ ▢ ▢ ▢ ▢
X ▢ X ▢ X
▢ ▢ ▢ ▢ X
▢ ▢ ▢ X X

Distractor grid 1:

▢ X X X ▢
▢ ▢ ▢ X ▢
X ▢ X X ▢
▢ X ▢ ▢ ▢
▢ ▢ ▢ X X

Distractor grid 2:

X ▢ X ▢ ▢
▢ X ▢ ▢ ▢
X ▢ X ▢ X
▢ ▢ X X ▢
▢ ▢ X X ▢

Instruction: Describe the target grid.
Generate the referring expression starting with the tag "Expression: " for the given target grid. Omit any other text.
Expression: The grid with a row of four X's at the top, a column of four X's on the right, and a diagonal line of X's from top-right to bottom-left.
assistant
Expression: The target grid has a unique pattern of filled cells, forming a central square and a smaller square on each side. The filled cells create a distinct shape, setting it apart from the distractor grids.
assistant