题目：
Some social workers _____ after the people in need while others ____ out food to the local people.
A．looked, gave
B．were looking, gave
C．were looking, were giving
D．looked, were giving
答案：
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下面是错误答案，用来干扰机器的。
(1)加热；黑色CuO变成红色，澄清石灰水变浑浊；； (2)二氧化碳；气球；酒精灯 (3)还原出的铜又被空气中的氧气氧化； (4)还原性；冶金
