以下是绝缘油界面张力检测所用铂圆环的周长，满足要求的是（）。
A.40mm
B.50mm
C.60mm
D.70mm
参考答案：A, B, C
We are all happy to find the exam much _________ than before.
A．easy
B．easily
C．more easily
D．easier
