给定如下Servlet代码，假定在浏览器中输入URL：http://localhost:8080/servlet/HelloServlet，可以调用这个servlet，那么这个Servlet的输出是（）。
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloServlet extends HttpServlet{
public void service(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException{
}
public void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.println("");
out.println("");
out.println("doGet Hello World!");
out.println("");
out.println("");
out.close();
}
public void doPost(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.println("");
out.println("");
out.println("doPost Hello World!");
out.println("");
}
}
a) 一个HTML页面，页面上显示doGet Hello World!
b) 一个HTML页面，页面上显示doPost Hello World!
c) 一个空白的HTML页面
d) 错误信息