引起输血发热反应，最常见的原因是
A．细菌污染
B．致热原
C．血型不合
D．红细胞破坏
E．过敏物质
参考答案：B
The archaeologists found gold coins and pottery in the lowest level of the site____ they reached three months ago．
A．what
B．for which
C．that
D．to which
机床一般规定累计运行（）h后，以操作工人为主，维修工人配合，对机床进行1次一级保养。
A.500
B.600
C.800
D.1000
