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 two vertical lines of X's in the middle columns, and X's in the top-left and bottom-right corners.
assistant
Expression: The target grid is the one with two filled cells at the top left corner, a filled cell in the middle of the second row and at the end of the second row, a filled cell in the second and third positions of the third and fourth rows, and a filled cell at the beginning and fourth position of the last row.
assistant