"My younger sister runs every night."

Translation: 我的妹妹每天晚上跑步。

[Tanicpanic]

The 的 should be optional, 我妹妹每天晚上跑步 should also be viewed as correct

[Alf42]

Hopefully they will fix this soon. It is still being marked incorrect to omit the 的 .

[Handrisuselo]

"每天晚上" can also be put before the subject!!!!

[Wadafik]

i don't understand the placement of subject and time. sometimes the subject goes first, sometimes not. can someone explain?

[Ted302303]

Both are correct, but Duolingo gives you wrong sometimes because they havent added both options as the correct answer.

我现在吃饭

现在我吃饭

has the same meaning and are equally good sentences.

See here for more information:

https://resources.allsetlearning.com/chinese/grammar/Time_words_and_word_order

[Wadafik]

ah, thanks. guess i should report it then.

[fede.frohlich]

Depends on the emphasis you want to give

[den-kungen]

妹妹is family, therefore 的, while quite understood, really ought not be there. I must say as somebody fluent in Chinese who just wants to see what the Net slang holds for me this proves quite difficult to find the exact sentence duolingo wants

[Megan345911]

Isn't 我妹妹每个晚上跑步。 correct?

[JanielleCh1]

的 is optional!