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参考答案：
参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】关于参考系的说法中正确的是（ ）
A.
参考系必须是静止不动的物体
B.
参考系必须是正在做匀速直线运动的物体
C.
参考系必须是固定在地面上的物体
D.
参考系是为了研究物体的运动而假定为不动的那个物体
【单选题】Naturally the young are more inclined to novelty than their elders and it is in their speech, as it always was, that most of the vocabulary changes originate. But listening critically to their talk I ...
A.
lack linguistic originality
B.
have always been interested in magic
C.
are becoming more superstitious
D.
are interested in magic when young