"I stood up immediately and turned on the light."
I think they should accept plain form. I wrote tsuketa instead of tsukemashita and was marked wrong.
I put "Sugu ni tatte, denki wo tsukemashita." and it was marked wrong. Is not putting the "watashi wa" that significant?
i just put that exact answer and it was marked as correct. i guess they updated it
All the lessons are looking for polite form, you should have known that by now.