若|a|=1，|b|=4，且ab＜0，则a+b=（ ）．
±3
科学管理阶段的代表理论有（）。
A.科学管理理论
B.管理过程理论
C.人类需要层次理论
D.人际关系学说
E.行政组织理论
On his way to the airport, it ________ him all of a sudden that he had forgotten her birthday. [ ]
A. hit
B. knocked
C. occurred
D. beat
