单项选择题

下面程序的功能是从键盘输入一行字符，统计其中有多少个单词，单词之间用空格分隔。请选择填空。
#include
       main()
       {
                     char s[80],c1,c2='';
                     int i=0,num=0;
                     gets(s);
                     while(s[i]!='\0')
                     {
                            c1=s[i];
                            if(i==0) c2='';
                            else c2=s[i-1];
                            if(_________) num++;
                            i++;
                     }
                     printf("There are %d words.",num);
       } A.
c1= =''&&c2= ='' B.
c1!=''&&c2= ='' C.
c1= =''&&c2!='' D.
c1!=''&&c2!=''