Translation:I opened the window, and then I closed it.
Ehh. I think that's too much paraphrasing for us to reasonably expect Duo to understand. It has to deal with enough possible translations already.
Lol it didn't accept "I opened a window, and then closed it." It has to be "THE" window!
Weird because it seems like a fruitless action or weird because you expected them to do something else after opening the window like yell at a cat?
I'm not a native speaker, so take this with a grain of salt, but i agree it feels weird using sorekara for an action that seems to go against the first action :s
て-form connects actions the same way と connects objects. The tense given at the end of the sentence applies for all the actions.
You can use て-form verbs to connect a sequence of actions (by the same subject); only the last verb needs to specify the tense, and the other verbs in the sequence will match that tense when you translate it to English.
The answer still demands a comma character which is not present. It's impossible to get by this sentence and go to next lesson. I have reported it, what more can I do?