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 ▢ ▢ ▢ X
X ▢ ▢ ▢ X

Distractor grid 1:

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

Distractor grid 2:

X ▢ ▢ ▢ X
X 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: A 5x5 grid with a solid horizontal line of 'X' in the middle row and 'X' at all four corners, while the rest of the cells are empty except for the corners. This grid uniquely features a complete middle row of 'X', which is not present in either of the distractor grids.
assistant
Expression: The grid with an X shape in the center surrounded by empty cells.
assistant