镇静钢的优点是什么？
参考答案：
镇静钢组织致密，强度高，偏析少，成份均匀。
—Do you really know _____ at this time yesterday?
— Sorry, I don't know. [ ]
A. what did they do
B. what they did
C. what were they doing
D. what they were doing
简述葡萄酒微氧技术的意义和作用？
