Q)14. Although one link in the chain was demonstrated to be weak, but not sufficiently so to require the recall of the automobile.
[A] demonstrated to be weak, but not sufficiently so to require
demonstrated as weak, but it was not sufficiently so that it required
[C] demonstrably weak, but not sufficiently so to require
[D] demonstrably weak, it was not so weak as to require
[E] demonstrably weak, it was not weak enough that it required

OA[spoiler] D
cant figure out between C and D. i dont understand usage of "as" [/spoiler]