如果执行下面C++代码后，输出的结果是"gesp ccf org cn "，则横线上应填入哪个代码？（ ）

#include <iostream>
using namespace std;
int main() {
    string str = "gesp.ccf.org.cn";
    string delimiter = ".";
    string result="";
    string token;
    size_t found = str.find(delimiter);
    while (found != string::npos) {
        token = str.substr(0, found);
        result += token;
        result += " ";
        __________________________ // 在此处填入代码
        found = str.find(delimiter);
    }
    //最后一部分
    result += str;
    result += " ";
    cout << result << endl;
    return 0;
}

{{ select(1) }}

• str = str.substr(found + delimiter.length(), str.length() - 1);
• str = str.substr(found, str.length() );
• str = str.substr(found, str.length() -1);
• 以上都不对