"Sir, I have a question."
Translation:Señor, yo tengo una pregunta.
La señora Sánchez - es amable.
El profesor es genial.
When talking about someone and include the title, you also include the definite article. This is just like it would be for a profession. This is quite common in other language; it's just that English doesn't do so for some reason.
Señora Sánchez, usted es amable.
Profesor, usted es genial.
If you're talking to the person directly, you don't use the article, just like you wouldn't do so for a profession.
The world is more or less round, but I'm not sure why you mention it. I'm also not sure whom you're addressing, hence let me state explicitly that this is a forum. A Duolingo forum is not the way to reach the contributors to a course if that's what you intended; for that, the report feature is better suited. The forum on the other hand is where you can converse with your fellow students.
What it is that your asking about isn't clear to me, as a fellow student. The best way to ask in a forum what is going wrong is to copy the question and your answer(s) here, and give your reasoning of why it would be correct, etc. We fellow students might be able to help you out, but of course we're limited in what we know, so the more information you give, the better the chance that at least one of us can figure out the problem.