A: 稀释浓硫酸
B: 探究可燃物燃烧的条件
C: 称量氯化钠
D: 验证质量守恒定律
用计算器计算:13﹣3.14≈____ (结果保留三个有效数字).
_____ Li Bai, a great Chinese poet, was born is known to the public, but some won’t accept it.
下列营养物质中,构成人体细胞基本物质的是( )