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一、单项选择题 下列各题均有4个选项,其中只有1个是正确的,请将正确选项的字母填入题后包括内。 1.星云是由气体和尘埃物质组成的,呈云雾状的天体,同恒星相比,星云的特点是:( ) A.质量大、体积大、密度大 B.质量大、体积大、密度小 C.质量小、体积小、密度大 D.质量小、体积小、密度小 2.6月22日—9月23日这一段时间,上海昼夜长短及其变化状况是:( ) A.昼长夜短,昼逐渐变长 B.昼短夜长,昼逐渐变长
First, single-choice multiple-choice questions The following questions have four options, of which only one is correct, please fill in the letters of the correct option after the title. 1. The nebula is composed of gas and dust material and is cloud-like. Compared with the stars, the nebula is characterized by: () A. High quality, large volume, high density B. High quality, large volume, and low density C. Small in quality, small in size and high in density D. Small in quality, small in size, and small in density From the period of 22nd to 23rd of September, the length of day and night in Shanghai and its changing conditions are: () A. Short and long nights,昼 gradually becomes longer B. 昼 昼 昼 昼