【单选题】

The primary function of the passage as a whole is to
A．(A) indicate the direction that research into a particular physical phenomenon should take

B．(B) illustrate the limitations of applying mathematics to complicated astrophysical phenomena
C．(C) clarify the differences between an old explanation of a physical phenomenon and a new model of it
D．(D) introduce a new explanation of a physical phenomenon
E．(E) explain the difference between two related physical phenomena