C'mon, guys. "It is obvious that you are tired" and "It is obvious you are tired" have EXACTLY the same meaning in English. Learning a language is not about direct, word-for-word translation, it's about communication.
And some English grammarians would scold anyone who put an unnecessary "that" in a sentence.
It is obvious you are tired is still being marked wrong. I have put in a report.
Agreed - "that" is optional in this sentence in English, and is not the way most people would say it