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 X
▢ ▢ ▢ ▢ X

Distractor grid 1:

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

Distractor grid 2:

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 where the first row is completely filled with "X", the second row has one empty cell at the beginning, and each subsequent row has an increasing number of empty cells from left to right, culminating in the last row which has all empty cells except for the last "X".
assistant
Expression: The target grid features a unique pattern of filled and empty cells, with a diagonal line of filled cells starting from the top-left corner and extending diagonally downwards, while the remaining cells are empty. This pattern distinguishes it from the distractors, which have different arrangements of filled and empty cells.
assistant