Can you specify which video? Some videos will start out blank / with nothing on the screen. Skip forward a few minutes into the video to see if there's anything.
I would leave it blank. Guessing an answer right means nothing and will mislead the analytics. Personally I just add .2 points to my total score for each unanswered question when computing my score. It takes out the random element.
@"Ron Swanson" What kind of timing strategies are you trying out? I tend to run out of time for RCs, pretty much leaving the fourth passage blank. I sometimes miss 1-2 questions on LRs depending on their difficulty levels.