轮缘高度不超过（）mm，用样板测量轮缘厚度磨损不超过原厚度的（）
A.20；20％
B.20；30％
C.30；20％
D.30；30％
参考答案：D
写出一个一元二次方程，使方程的一个根为2，则这个方程可能为（ ）。
While enjoying himself in the amusement theme park, he heard a loud cry of pain; he _____ himself
around and ______ to see a girl had fallen off the swing and was crying for help. [ ]
A. turned; terrified
B. swung; was terrifying
C. turned; was terrifying
D. swung; was terrified
