Which of the following expresses the possible number of positive real solutions for the polynomial equation shown below?

x³-4x²-7x+28=0

a. two or zero

b. three or one

c. one

d. two

The answer is to this question is letter "B. three or one". All of the roots of this equation could be real numbers. The imaginary roots come in pairs, one being the conjugate of the other. Thus, leaving only 1 of the roots real.