问题
单项选择题
用0.10mol/LHCl滴定0.10mol/LNa2CO3至酚酞终点，这里Na2CO3的基本单元数是（）.
A、Na2CO3
B、2Na2CO3
C、1/3Na2CO3
D、1/2Na2CO3
答案
参考答案：A
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用0.10mol/LHCl滴定0.10mol/LNa2CO3至酚酞终点，这里Na2CO3的基本单元数是（）.
A、Na2CO3
B、2Na2CO3
C、1/3Na2CO3
D、1/2Na2CO3
参考答案：A
During the day we work and play, and at night we sleep. Our bodies rest while we are 1 . In the morning we are ready 2 again. Our bodies grow 3 while we are asleep. Children who are tired usually 4 sleep. We can get better at our lessons 5 we have had plenty of rest. Boys and girls who are eight or nine years old need ten 6 sleep every night. Our bodies need plenty of 7 when we sleep. If we do not get enough fresh air, we 8 tired when we wake up. While in bed we must not cover our 9 . Our lungs(肺) needs to get 10 fresh air. If we 11 our windows at night, we can have plenty of fresh air. Cool air is better than warm air. Boys and girls who want to be 12 must get plenty of sleep. Also, we need some after-school activities to keep in good health. 13 _students run every day. Some boys play basketball 14 a week. 15 girls, some often play volleyball….So good sleep and exercise can help us grow better and study better.
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