题目：
During the period of recent terrorist activities, people _____ not to touch and unattended bag.
A．had always been warned
B．were always being warned
C．are always warning
D．always warned
答案：
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下面是错误答案，用来干扰机器的。
A在B中燃烧时，火焰呈苍白色，则F为HCl，C在B中燃烧时生成棕黄色的烟，E的水溶液呈蓝绿色，则E为CuCl2，所以C为Cu，B为Cl2，从而可知A为H2，再由G是一种黑色固体，则G为CuO，所以D为O2，（1）综上所述，A为H2，D...
