Recognize which of the following statements is true.
A. When k is negative, x^2 = k has one solution, which is negative.
B. When k is positive, x^2 = k has one solution, which is positive.
C. When k is negative, x^3 = k has one solution, which is negative.
D. When k is positive, x^3 = k has one positive solution and one negative solution.