Stay awake!You should know that it________to sleep in class. [      ]

A. doesn't permit  

B. is not permitted

C. will not be permitted  

D. was not permitted

下面是复数类complex的定义，其中作为友元函数重载的运算符“--”的功能是将参数对象的实部减1，然后返回对该对象的引用；请补充完整。 class complex { private: int real; iht imag; public: complex(int r=0,int i=0):real(r),imag(i) {} void show() { cout＜＜real＜＜(imag＜0"-" :"+")＜＜imag＜＜’i’; } 【15】 ; }; complex& operator -- (complex &c) { c.real--; return c; }