Answer
true
Work Step by Step
RECALL:
In the complex number $a+bi$, $a$ is the real number part while $bi$ is the imaginary number part.
Note that when $b=0$, the complex number $a+bi$ becomes $a+oi=a$, which is a real number.
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This means that the set of real numbers is a subset of the set of complex numbers.
Thus, the given statement is true.