Vertical means vertical. The question is to ask which of the five options is perpendicular to the straight line given in the question. This topic is very simple. I only know that the slopes of two vertical lines are negative reciprocal, so the answer is D.
Give me another question.
θ is an acute angle. Given the value of sinθ, what is cosθ? The topic itself is very simple, and it examines the double-angle formula: cos2θ= 1-2sin? θ
So it can be calculated that the answer is a.