Question

construct the line that is perpendicular to l at point a.

Explanation:

Step1: Recall perpendicular - line property

Perpendicular lines form a 90 - degree angle.

Step2: Identify the correct figure

The figure where the blue - drawn line and line $\ell$ form a right - angle (90 degrees) at point A is the correct one.

Answer:

The third figure (the one with the blue line forming a right - angle with line $\ell$ at point A)