当如果气缸的点火正时在延迟了6度后（）秒依然存在爆燃，ECM会让发动机停机。
A.4
B.5
C.6
D.7
参考答案：B
—Is Mr Smith swimming in the pool, Harry?
—It _____ be him. I saw him go to the library just now. [ ]
A. may not
B. can't
C. needn't
D. mustn't
进行因子分析的前提条件是，各变量之间应该（）。
A.相互独立
B.低度相关
C.高度相关
D.完全相关
