10. A satellite revolves around a planet in an elliptical orbit and experiences only the gravitational force. If the satellite's speed at point a is 8000 m/s, the satellite's speed at point c is
(A)8000 m/s
(B)6000 m/s
(C)4000 m/s
(D)2000 m/s

(E)1000 m/s

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