If the mirror is placed on the line AB, then which of the answer figures is…

Concept: When a mirror lies along a horizontal line beneath a figure, the mirror image is obtained by flipping the whole figure top-to-bottom about that line: each point's vertical position reverses while its left-right position stays the same. An element near the top of the original moves an equal distance below the line (and vice versa); the vertical component of any slanting arrow reverses direction; and a shape stays on the same left/right side of the figure, only its up-down position and internal orientation flip.

Application:

• The small trapezoid sits in the upper half of the original figure, so after the flip it moves down to occupy the same relative distance in the lower half of the circle.

• The diagonal line originally points down-and-to-the-left, with its arrowhead in the lower half; after flipping about the horizontal mirror line it points up-and-to-the-left instead, because the vertical part of its direction reverses.

• The horizontal line carrying the small tick mark stays in the middle-left region, since a horizontal element is unchanged by a flip about a horizontal line.

• The triangle-in-capsule shape stays attached to the same (right) side of the circle, but the triangle inside it — originally pointing upward — now points downward, since it flips vertically along with everything else.

Cross-check: Comparing this predicted figure with the four answer figures, only one keeps the trapezoid in the lower half, shows the diagonal arrow now pointing up-and-left, leaves the tick-marked line horizontal in the middle-left region, and shows a downward-pointing triangle inside the right-side capsule — every other figure repositions or restyles at least one element incorrectly, or gets the arrow's direction wrong.

Result: So the figure with the trapezoid in the lower half, the diagonal arrow pointing up-and-left, the unchanged tick-marked horizontal line on the left, and a downward triangle inside the right-side capsule is the correct mirror image.