关于sc的一道题~求助

sjjay

10. Climatic shifts are so gradual as to be indistinguishable at first from ordinary fluctuations in the weather.
(A) so gradual as to be indistinguishable
(B) so gradual they can be indistinguishable
(C) so gradual that they are unable to be distinguished
(D) gradual enough not to be distinguishable
(E) gradual enough so that one cannot distinguish them
i choose c.the answer is a.
        
i remember og said so...as.. should be apply in negtive sentence.such as  not so...as....;could de anyone help me ?why the A is right?

SHJDHKBB9

A在本题目中无错误且比C简洁因而选A.

OG的讲解需要在不同情况下不断转换.

sjjay

查了一下资料，此处短语为 so...as to 表结果。并非og 说的 as...as.. 和not  so....as.....

当选 a

多谢s兄的回答，确实需要灵活掌握啊

cician

C错在unable,不能说gradual unable啊。另外，so... as to ....做如此。。。以至于的时候中间只能加adj或者adv就目前情况看