The shape that cannot be formed with side lengths 9mm, 9mm, 9mm, 9mm is a trapezoid.
A trapezoid must have at least one pair of parallel sides. Since all four side lengths are the same, none of the pairs of sides are parallel, and thus the figure cannot be a trapezoid.
A rectangle must have four right angles. Since all four side lengths are the same, the figure is a square, and all four angles are right angles, so the figure can be a rectangle.
A parallelogram must have two pairs of parallel sides. Since all four side lengths are the same, two pairs of sides must be parallel, so the figure can be a parallelogram.
A rhombus must have four congruent sides and all four angles must be congruent. Since all four side lengths are the same, the figure has four congruent sides, but the angles are not necessarily congruent, so the figure cannot be a rhombus.
Thus, the shape that cannot be formed with side lengths 9mm, 9mm, 9mm, 9mm is a trapezoid.
Complete question:
Which shape could NOT have side lengths 9mm,9mm,9mm,9mm ? (A) trapezoid (B) rectangle (C) parallelogram (D) rhombus