有一个弱弱的问题

so..as是只能用于否定句，而as..as既可用于肯定也可用于否定句，正如这题，对吗

1.        Never before had taxpayers confronted so many changes at once as they had in the Tax Reform Act of 1986.

(A) so many changes at once as they had in

(B) at once as many changes as

(C) at once as many changes that there were with

(D) as many changes at once as they confronted in（D）

(E) so many changes at once that confronted them in

对。

参见Section 21 A, in Thomson, A.J. and Martinet, A.V. (1999) A Practical English Grammar (4th ed., in Chinese) 外语教学与研究出版社。P55。