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 ▢ ▢

Distractor grid 1:

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

Distractor grid 2:

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: The grid with Xs in the corners and a single X in the middle of each of the bottom three rows.
assistant
Expression: ▢▢▢▢▢

This expression refers to the target grid by specifying the location of the empty cells, which are marked with "▢". The expression starts with "▢▢▢▢▢" to indicate that the top-left, top-right, bottom-left, and bottom-right cells are empty. This uniquely identifies the target grid among
assistant