大全补充250-91，不懂，请高手指点。谢
91. 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
答案B
我的疑问是:B中的that指代什么？
如果指代mass，则逻辑意思不通。因为，比较的就是The distribution of mass within the core of the Earth和) mass within the mantle surrounding the core
但是，如果指代distribution ，则distribution within the mantle surrounding the core也不通阿。
请指点！ | 
