闭门留寇
参考答案：
解析：对于外邪未尽或邪实而不虚的病证，治疗上宜以祛邪为主。若误用收涩或补益药物，则可使病邪内留，病情加重，称为闭门留寇。
The symmetry principle refers to the idea that if an economy is organized under a fair set of rules:（）
A. the greatest good is achieved for the greatest number of people.
B. the wealth that individuals accumulate will become equal over time.
C. individuals receive goods and services equal in value to their economic contribution.
小明家最近装了一台如图所示的“光电互补型”太阳能热水器。该热水器晴天以吸收太阳能作为加热方式，阴雨天可用电加热方式。
（1）太阳能热水器贮满水，水温从20℃加热到70℃时需要吸收多少热量？
（2）若在雨天使用电热器将一满箱水从20℃加热到70℃，加热器正常工作了7h，则此热水器的效率为多少？
