试剂中含有微量被测组份所引起的误差属于（）。
A.偶然误差
B.相对偏差
C.系统误差
D.绝对误差
参考答案：C
I couldn't have got to the meeting on time - _______ an earlier train .
A．if I had not caught
B．unless I had caught
C．if I did not catch
D．unless I caught
基准孔的基本偏差代号是（）。
