The correct answer is B. Complex.
Imaginary numbers are a subset of complex numbers, which are numbers that can be expressed in the form \( a + bi \), where \( a \) and \( b \) are real numbers and \( i \) is the imaginary unit (where \( i^2 = -1 \)). Real numbers are also part of complex numbers when \( b = 0 \) (e.g., the real number \( a \) can be written as \( a + 0i \)). However, imaginary numbers specifically are not real numbers, so they are not a subset of real numbers.