According to the speaker, what makes family portraits valuable to historians？
A. They are few in number.
B. They depict important historical events.
C. They provide a lot of information about ordinary people.
D. They conceal clues about the social role of artists.
固定资产折旧方法的变更，属于会计政策的变更。()
A. 正确
B. 错误
如图所示，一平面波在介质中以速度u=20m/s沿，轴负方向传播，已知A点的振动方程，为y=3COS 4πt(SI)，以A点为坐标原点的波动方程为()。
A. y=3cos(4πt-x/20)
B. y=3COS4π(t+x/20)
C. y=3COS 4π(t-x/20)
D. y=3cos(4πt+x/20)
企业自行建造固定资产过程中发生的、非正常原因造成的单项工程或单位工程报废或毁损的净损失应计入当期营业外支出。()
A. 正确
B. 错误
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