KVPY SA Exam 2013 Question Paper

Let a,b be non-zero real numbers. Which of the following statements about the quadratic equation $\mathit{a}{\mathit{x}}^2+\left(\mathit{a}+\mathit{b}\right)\mathit{x}+\mathit{b}=0$ is necessarily true?
(I) It has at least one negative root.
(II) It has at least one positive root.
(III) Both its roots are real.