[求助]XDF补充材料 语法部分section3-4

4. Developing nations in various parts of the world have amassed $700 billion in debts; at stake, should a significant number of these debts be repudiated, is the solvency of some of the world’s largest multinational banks.

(A) should a significant number of these debts be repudiated, is

(B) should a significant number of these debts be repudiated, are

(C) should they repudiate a significant number of these debts, are

(D) if there is a repudiation of a significant number of these debts, would be

(E) if a significant number of these debts will be repudiated, is

答案是A?

不知为什么？