Question

which of the following will map $\triangle abc$ onto $\triangle abc$?
counterclockwise turn $90^{\circ}$ about the origin
translation 2 units right and 1 units up
reflection in the $x$-axis
clockwise turn $90^{\circ}$ about the origin

Explanation:

Each point in $\triangle ABC$ maps to $\triangle A'B'C'$ by flipping over the x-axis: for any point $(x,y)$, it becomes $(x,-y)$, which matches the vertical mirroring seen in the grid.

Answer:

reflection in the x-axis