参考答案

正确答案：B
解析："This is a phase change (liquid to gas) which is a physical change." Because this example of a physical change is provided, it must be concluded that phase changes are sometimes physical changes. Choice A is not correct because the example is a physical change, not a chemical change. Choice C is not correct because the quantity of a substance (extensive properties) is not mentioned in the discussion on phase changes. Choice D is not correct because in a physical change the fundamental composition of a substance has not changed.