请高手帮忙翻译一句话， 关于not so ...as

这句话理解不了，请高手帮忙翻一下，不胜感激

Child prodigies are marked not so much by their skills but instead by the fact that these skills are fully developed at a very early age.

(A) but instead

(B) rather than

(C) than

(D) as（D）

(E) so much as

The idiomatic form for this kind of statement is not so much by X as by Y. Hence, D is correct. Each of the other options produces an unidiomatic statement. This question is of middle difficulty

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not so much .. as  固定用法.  与其... 不与

多谢，呵呵，我把当not as ....as 理解了