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
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
D
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。