In the figure, which pair of angles are vertical angles? 
A$\angle a$ and $\angle b$
B$\angle b$ and $\angle c$
C$\angle a$ and $\angle c$
D$\angle c$ and $\angle d$
Answer & Solution
Correct answer: C. $\angle a$ and $\angle c$
Vertical angles are the opposite angles formed when two lines intersect. In the figure, $\angle a$ and $\angle c$ are opposite each other, so they are vertical angles and therefore equal.
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