A satellite S is moving in an elliptical orbit around the earth. The mass of the satellite is very small compared to the mass of the earth. Then,

• A

  the linear momentum of S remains constant in magnitude.

• B

  the acceleration of S is always directed towards the centre of the earth.

• C

  the angular momentum of S about the centre of the earth changes in direction, but its magnitude remains constant.

• D

  the total mechanical energy of S varies periodically with time.