Choose the correct phrase to complete the gamer's text message to her friend.

My eyes were completely red and my thumbs ached. I ___ that new fantasy game for six hours straight when you finally called!

The correct answer is had been playing.

We use the past perfect continuous (had been playing) to talk about an action that was ongoing up to a specific moment in the past (when the friend called). The phrase "for six hours straight" emphasizes the duration of this past action. "Was playing" doesn't capture the accumulated duration before the call as effectively.