OG41，以前的帖子没解决我的问题

41. Under a provision of the Constitution that was never applied. Congress has been required to call a convention for considering possible amendments to the document when formally asked to do it by the legislatures of two-thirds of the states.
(A) was never applied, Congress has been required to call a convention for considering possible amendments to the document when formally asked to do it
(B) was never applied, there has been a requirement that Congress call a convention for consideration of possible amendments to the document when asked to do it formally
(C) was never applied, whereby Congress is required to call a convention for considering possible amendments to the document when asked to do it formally
(D) has never been applied, whereby Congress is required to call a convention to consider possible amendments to the document when formally asked to do so
(E) has never been applied. Congress is required to call a convention to consider possible amendments to the document when formally asked to do so

答案：E

Choices A, B, C, and D contain tense errors (the use of was never applied with has been required in A, for example), unidiomatic expressions (call... for considering), and uses of a pronoun (it) with no noun referent. By introducing the subordinating conjunction whereby, C and D produce sentence fragments. Only E, the best choice, corrects all of these problems. The predicate has never been applied refers to a span of time, from the writing of the Constitution to the present, rather than to a past event (as was does), and the phrase is required indicates that the provision still applies. The phrase call... to consider is idiomatic, and to do so can substitute grammatically for it.

请问，whereby不是有副词的词性吗？为什么会造成sentence fragments？

Under a provision, whereby congress is required to call a convention.

whereby 后面的句子不是主句， 所以整个句子缺少句子主干（主谓宾）。