再问大全738，怎么理解它的时态

738.The Emperor Augustus, it appears, commissioned an idealized sculptured portrait, the features of which are so unrealistic as to constitute what one scholar calls an “artificial face.”

(A) so unrealistic as to constitute

(B) so unrealistic they constituted

(C) so unrealistic that they have constituted

(D) unrealistic enough so that they constitute（A）

(E) unrealistic enough so as to constitute

738, og-088, sec08-22

The verbs are and calls indicate that the sculpture is being viewed and judged in the present. Thus, neither the past tense verb constituted (in B) nor the present perfect verb have constituted (in C) is correct; both suggest that the statue’s features once constituted an artificial face but no longer do so. Also, B would be better if that were inserted after so unrealistic, although the omission of that is not ungrammatical. Choices D and E use unidiomatic constructions with enough: unrealistic enough to constitute would be idiomatic, but the use of enough is imprecise and awkward in this context. Choice A, which uses the clear, concise, and idiomatic construction so unrealistic as to constitute, is best。

我想知道，为什么解释说答案C的完成时和B的过去式用的不好？我不是很明白ETS对在这里的分析。请解答：）

如果排除时态问题，我觉得C和A从语法角度说都是没有错的，A优于C就是因为简练，可以这么理解吗？

请指点，谢谢