二、多项选择题（本大题共5小题，每小题2分，共10分）

在每小题列出的五个备选项中至少有两个是符合题目要求的，请将其代码填写在题后的括号内。错选、多选、少选或未选均无分。

21.下面属于合法的C标识符有(          )

A._123                                                      B．abc

C．123_                                                   D．abc.c

E．ab_123

22.若所用变量已正确定义，以下各程序段执行后，变量x值相等的有(          )

A．x=0;                                                    B．x=0；i=0；

for (i=0;i<=3;i )                     while(i<3)

x=i x;                           {   x=i x；

                                          i ；

}

C．for（i=0；i<5；i ）                        D．x=0；i=0；

x=i x;                          lop： x=i x；

                                            i ；

                                             if( i < =3) goto lop;

E．i=0；x=0；

do{ x=x i；i=i 1；

}while(i<=3);

23.设有声明int x[5]={2,4,6,8,10）；下面表达式的结果为2的有(          )

A.a[o]                                                       B.a[3]-a[2]

C.(a[4]-a[2])/2                                           D.a[3]-a[0]

E.a[0]/2 a[l]/4

24.设有如下定义及赋值：

int a[5]={1,2,3,4,5), * p;

p=a;

则可以输出元素值为3的语句有(          )

A. printf (＂%d\n＂,a 2);                           B.printf (＂%d\n",p 2);

S. printf (＂%d＼n＂,p[2]);                        D.printf (＂%d＼n＂,* (p 2));

E. printf (＂%d＼n＂,a[3]);

25.下面关于结构体类型的定义正确的有(          )

A. struct ABC                                            B.struct tree

{                                   {

int a,                                int branch;

char b,                              char name[20];

char * p,                             char * relation;

};                                  };

C. struct ABC                                            D.struct tree

{                                                              {

int a;                                                         intbranch,

char b;                                                      charname[20],

char *p ;                                                   char*relation,

};                                                             };

E. struct

{

char name[20];

int weight;

int sex;

};