My friend goes to work by bus.
Does my friend go to work by bus? (общий)
Does my friend go to work by bus or by car? (альтернативный)
Why does my friend go to work by bus? (специальный)
Who goes to work by bus? (к подлежащему)
My friend goes to work by bus, doesn't he? (разделительный, может быть, тоже нужен)