In triangle GHI, the height is the perpendicular line from the opposite vertex to the given base.<br><br>
&bull; From the figure: GI is the base.<br>
&bull; The height must be the perpendicular line from the opposite vertex (H) to GI.<br>
&bull; HI is perpendicular to GI (the triangle has a right angle at I).<br><br>
Final Answer: A: HI