要实现从MainActivity活动跳转到FirstActivity活动,需要在MainActivity中定义一个意图Intent对象,并启动从该意图实现跳转。则下列用Java语言表示正确的是_________________ (3.0分) A. Intent intent=new Intent(MainActivity.this,FirstActivity.class); startActivity(intent); B. Intent intent=new Intent(this,FirstActivity.class); startActivity(intent); C. Intent intent=new Intent(FirstActivity.class,MainActivity.this); startActivity(intent); D. Intent intent=new Intent(FirstActivity.class,this); startActivity(intent);