How and why Jack came to China not known. When and where to build the new librar
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How and why Jack came to China _____ not known. When and where to build the new library _____ not been decided.
A. is; has B. are; has C. is; have D. are; have
试题答案
A
两个引导词是一个抽象概念时，谓语动词用单数形式。