在化学反应中，反应物的总质量与生成物的总质量总是相等的，这体现了定律。
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Correct answer
B. 质量守恒
Principle or equation
质量守恒定律：化学反应前后各物质的质量总和相等。
Why this answer is correct
质量守恒定律是化学基本定律，适用于所有化学反应。
Example
2H₂ + O₂ → 2H₂O中，反应物总质量等于生成物总质量。
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