the answer is complex number
a complex number is 2 parts
1. the real part
2. the imaginary part
the real part is the 'a' part of the a+bi
the imaginary part is the 'bi' part of the a+bi
answer is A
(B means exponent is no higher than 1, C means exponent is 2, D means b^2-4ac)
answer is A
