单选题下列判断正确的是（ ）．A物体的体积越大，密度越小B燃料的质量越大，热值越大C使用杠杆必定省力D雾凇和霜都是水蒸气凝华形成的
单选题
下列判断正确的是（ ）．
A
物体的体积越大，密度越小
B
燃料的质量越大，热值越大
C
使用杠杆必定省力
D
雾凇和霜都是水蒸气凝华形成的
参考解析
解析：
A项，质量相同的物体，体积越大，密度越小；B项，热值是燃料的一种属性，由燃料的种类决定，不受燃料质量的影响；C项，杠杆有三类：省力杠杆、费力杠杆和等臂杠杆，使用杠杆不一定省力；D项，雾凇和霜都是固态，都是由空气中的水蒸气遇冷放热直接变为固态小冰晶形成的，都属于凝华现象．
A项，质量相同的物体，体积越大，密度越小；B项，热值是燃料的一种属性，由燃料的种类决定，不受燃料质量的影响；C项，杠杆有三类：省力杠杆、费力杠杆和等臂杠杆，使用杠杆不一定省力；D项，雾凇和霜都是固态，都是由空气中的水蒸气遇冷放热直接变为固态小冰晶形成的，都属于凝华现象．
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