单项选择题

设有以下定义和程序：
#include＜iostream.h＞
class A1public：
void show1()
cout＜＜"class A1"＜＜endl；
;
class A2 : public A1public:
void show2()
cout＜＜"class A2"＜＜end1
;
class A3 : protected A2public:
void show3()
cout＜＜"class A1"＜＜endl;
;
void main() A1 obj1;
A2 obj2;
A3 obj3; 则以下不合语法的调用语句是

A．obj1. showl()；
B．obj2. showl()；
C．obj3. showl()；
D．obj2. show2()；

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单项选择题

有以下程序：#include ＜iostream＞#include ＜math＞using namespace std;class pointprivate: double x; double y;public: point(double a, double b x=a; y=b; friend double distance (point a, point b ; ;double distance(point a, point b return sqrt((a. x-b. x )*(a. x -b. x )+ (a. x -b. x)*(a. x-b. x));int main () point p1(1,2); point p2(5,2); cout＜＜distance (p1, p2)＜＜end1; return 0; 程序运行后的输出结果是

A．1
B．5
C．4
D．6

单项选择题

有以下程序#include ＜iostream＞using namespace std:class Baseprivate: char c;public: Base(char n) :c(n) ～Base ( ) cout＜＜c;; class Derived : public Baseprivate: char c;public: Derived(char n):Base(n+1),c(n) ～Derived() cout＜＜c;;int main() Derived obj(’x’); return 0; 执行后的输出结果是

A．xy
B．yx
C．x
D．y

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