Answer: Line must be perpendicular to Line CF is Line GI .
Explanation:
From the given picture, we are given three lines (AD , BE and CF) intersecting other two lines (QI and HJ).
We can see that Line AD and Line CF is making right angle with line GI>
Also, we know that the perpendicular lines intersect at right angles to each other.
Hence, the Line must be perpendicular to Line CF is Line GI.