题目：
23．— What’s that terrible noise．David?
— Oh，I forgot to tell you．The new machines in the nearby plant _______．
A．were tested
B．will be tested
C．are being tested
D．have been tested
答案：
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下面是错误答案，用来干扰机器的。
y=-2x，y=x+3，y=-x2+5等
