使用圆规画圆时，应尽可能使钢针和铅芯垂直于（）。
A、纸面
B、圆规
C、比例尺
D、直线笔
参考答案：A
Though________this time, I was not discouraged and made up my mind to try again the next time. [ ]
A. beaten
B. beating
C. having beaten
D. being beaten
当a=1，b=2时，代数式a2﹣ab的值是( )
