Mary _____ six dollars on the pen. [ ]
A. spent
B. paid
C. cost
D. took
答案：A
二次函数y=-3x2+5x-6的图象的开口方向是______．
MyClock 类的拷贝构造函数的声明语句为( )。
A．MyClock&(MyClock
B．MyClock(MyClock
C．MyClock(MyClock &
D．MyClock(MyClock *
