Which of the following systems are stable or unstable?

(a) G(s)=1/[(s + 5)(s + 2)],
(b) G(s)=1/[(s − 5)(s + 2)],
(c) G(s)=1/[(s − 5)(s − 5)],
(d) G(s)=1/(s² + s + 1),
(e) G(s)=1/(s² − 2s + 3).