Mark has spent three hours playing a computer game. He's been sitting there for three hours. It was two o'clock when Mark started the game. He's been playing since two o'clock. Three hours have passed since Mark and Sarah got up from the lunch table. They finished their lunch three hours ago. B For and since with the present perfect We often use for and since with the present perfect to talk about something continuing up to the present. FOR SINCE We use for to say how long something has continued. I've been waiting for forty minutes. We've known about it for two days. Melanie.
