Answer
$\text{real, imaginary, imaginary unit}$
Work Step by Step
Recall:
In the complex number $a + bi,$ $b$ is called the real part while $b$ is called the imaginary part, and $i$ is called the imaginary unit.
Thus, the missing expressions in the given statement, in order, are:
$$\text{real; imaginary; and imaginary unit}$$
