"Walaupun saya kecil, badan saya kuat." = not accepted
Dear Duolingo, would you please be so kind to accept this as an alternative correct answer ?
"walau"= "walaupun" , mean the same.
Why is badanku not acceptable?
You probably used "saya" earlier in the sentence, so you would be mixing two levels of formality.
Kamu benar. I made the same mistake and also wondered why.