3. The distribution of mass within the core of the Earth, like the mantle that surrounds the core, has been deduced from the orbital behavior of the Earth and the motions of satellites controlled by the gravity of the Earth.
(A) the mantle that surrounds the core
(B) that within the mantle surrounding the core
(C) that of the mantle surrounding the core
(D) the mantle the core surrounds
(E) the distribution of mass within the mantle that surrounds the core

Can any one tell what is the OA and how to deduce
I found A correct.