he head of the company promised to deal with matters of   this sort ________ he returned to his office.   [ ]

A. until                        

B. while       

C. by the time                    

D. the moment

设函数f(x)，g(x)在a点的某邻域内二阶可导，且f(a)=g(a)=0，f’(a)＜0．g’(a)＞0，令

，则

A．x=a是φ(x)的极小值点．
B．x=a是φ(x)的极大值点．
C．(a，φ(a))是曲线y=φ(x)的拐点．
D．以上都不对．