下列现象中，物质的密度发生变化的是 [ ]
A.一杯水倒掉一半
B.水中加些食盐
C一.张纸被撕成两半
D.粗铜丝拉伸后变成了细铜丝
答案：B
I would have come earlier, but I ________ that you were waiting for me.
A．didn’t know
B．hadn’t know
C．would have known
D．haven’t known
在学习《藤野先生》时，为了让学生了解叙事散文的特点，教师列举了同类的散文。下列文章中不能用来举例的是（）。
A.《从百草园到三味书屋》
B.《阿长与山海经》
C.《背影》
D.《紫藤萝瀑布》
