铬化合物中六价Cr毒性最大，有强刺激性，引起蛋白变性，干扰酶系统。
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Which of these statements best describes VPLS？（）
A. Neither broadcast nor multicast traffic is ever flooded in VPL
B. Multicast traffic is flooded but broadcast traffic is not flooded in VPL
C. VPLS emulates an Ethernet switch， with each EMS being analogous to a VLA
D. Because U-PE devices act as IEEE 802.1 devices， the VPLS core must use ST
E. When the provider experiences an outage， IP re-routing restores PW connectivity and MAC re-learning is needed.
游戏的社会性本质观认为游戏是儿童的一种本能活动。
A. 正确
B. 错误
在PowerPoint2010中动画有两种形式，一种是（），另一种是（）。
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