什么叫焊接裂纹？
参考答案：
焊接裂纹就是在焊接应力及其它致脆因素的共同作用下，焊接接头局部地区的金属原子结合力遭到破坏而形成的新界面而产生的缝隙。
观察DNA和RNA的分布时，下列哪项操作是正确的[ ]
A．染色时先用甲基绿染液染色，再滴加吡罗红染液
B．将涂片用8%的盐酸处理后，接着用染色剂染色
C．观察时应选择染色均匀、色泽较浅的区域
D．先用低倍物镜找到较清晰的细胞，然后换上高倍物镜
The house rent is expensive. I've got about half the space I had at home and I am paying ______ here.[ ]
A. as three times much
B. as much three times
C. much as three times
D. three times as much
