请教885 sec b -10

10.   The work of mathematician Roger Penrose in the early 1970s, on the geometry of what are called aperiodic tiles, turned out to describe the architecture of a previously unknown class of crystals.

(A) what are called aperiodic tiles, turned out to describe

(B) what is called aperiodic tiles, describes

(C) aperiodic tiles, describing

(D) so-called aperiodic tiles, describe（A）

(E) aperiodic tiles, it turned out to describe

这道题目我看了以前很多讨论，但还不是很理解，查过字典关于turn out，有prove to be, “原来是，证明是”的含义，这里是否因为要表达这种意思所以要保留turn out呢，就和remain, become等词一样，还请各位赐教。

个人理解，turn out在此题中有一种前后contrast的语意。