Past Simple or past continuous?

Hello,

I have a fill in the blanks question about past simple and past continuous tenses. I think blanks might be suitably filled with past continuous tenses to indicate two parallel progressive actions in the past. However, I'm not sure about whether past simple is suitable or not.

Here's the question:

"Our teacher_was downloading____(download) our first homework assignments while we__were uploading___(upload) our second assignments. "

Thanks,