The problem he referred to _____ difficult, but is isn’t at all.

A．must be

B．seeming

C．seems

D．seem

下面程序的预设功能是：统计文件abc.txt中的字符个数。
#include ＜iostream.h＞
#include ＜fstream.h＞
#include ＜stdlib.h＞
void main()

fstream file;
file.open( "abc.txt", ios::in);
if ( !file )

cout＜＜"Can not open abc.txt"＜＜end1;
abort();

char ch;
int i = O;
while (______________)

file.get(ch);
i++;

cout＜＜"Characters : "＜＜i＜＜end1;
file.close();

则程序中空白处应该填入的语句是 【15】 。