第20题: [单项选择]Broad sanctions that ______ Indian and Pakistani scientists from the West are a counterproductive response to the two nations' unwelcome arrival in the nuclear club. A. could isolate B. may isolate C. isolated D. isolate 参考答案:A 答案解析:[注释]谓语动词需要过去时情态动词 could 在句中的搭配。