单项选择题

阅读下面程序 public cmass ThreadTest {  public static void main(String args[]) {   Thread t1=new Thread(new Hello());   Thread t2=new Thread(new Hello());   t1.start();   t2.start();  } } class Hello implements Runnable {  int i;  public void run() {   while(true) {    System.out.println("Hello"+i++);    it(i==5) break;   }  } } 此程序创建线程所使用的方法是

A.继承Thread类
B.实现Runnable接口
C.t1.start()
D.t2.start()