填空题 Think hard, and you'll have an idea. ______ think hard, you'll have an idea.
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【正确答案】 1、{{U}}If you{{/U}}    
【答案解析】[解析] 对比填空：句子中缺少条件状语从句的引导词if，If+主语，所以正确答案为If you。注意首字母要大写。