哪种数据变换的方法将数据沿概念分层向上汇总？（）
A.平滑
B.聚集
C.数据概化
D.规范化
参考答案：C
This printer is of good quality.If it ________ break down within the first year，we would repair it at our expense.
A．would
B．should
C．could
D．might
柴油闪点控制在不小于（）℃。
A.50
B.55
C.60
D.67
