钢依是否加入合金元素可分为（）。
A、镇静钢
B、沸腾钢
C、碳素钢
参考答案：C
She is a strong-willed woman and not once _____ in to any difficulty in her life. [ ]
A. she has given
B. did she give
C. she gave
D. has she given
酸雨观测中，K值是电导率仪进行3次读数的平均值换算到________时的值。
A．0℃
B．20℃
C．25℃
