If two adjacent angles form a linear pair, which statement is always true? 
AThey are equal
BThey are complementary
CThey are supplementary
DThey are vertical angles
Answer & Solution
Correct answer: C. They are supplementary
A linear pair consists of two adjacent angles whose non-common arms are opposite rays. Therefore their sum is $180^{\circ}$, so they are supplementary. They need not be equal, complementary, or vertical.
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