题目

The three nations were wise enough not ____the agreement until they could discuss it further. A. to sign       B. signing          C. having signed     D. to have signed 答案：D 解析: 考查非谓语动词。句意：这三个国家足够明智，直到他们进一步磋商之后才签订这个协议。enough之后必须跟动词不定式，而动词不定式的动作要早于句子谓语动词were之前先发生，所以应该使用动词不定式的完成形式。

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