Consider the equation `10 z^2-3i z-k=0,w h e r ez` is a following complex variable and `i^2=-1.` Which of the following statements ils true? (a)For real complex numbers `k` , both roots are purely imaginary. (b)For all complex numbers `k` , neither both roots is real. (c)For all purely imaginary numbers `k` , both roots are real and irrational. (d)For real negative numbers `k` , both roots are purely imaginary.