I am working on my AS in IT and am currently taking introduction to web development. We just started classes and finished our first unit. We are at the moment learning HTML5. For our first unit we created a basic setup of HTML for our homepage. According to the reading and assignment my code was to look like this:

<!DOCTYPE html>

Now here is the part that is bothering me. I got a 100 on the assignment but the professor told me I needed to take out the second line of <html>. I like to understand things and want to understand why this would need to be taken out. In my understanding the DOCTYPE gives the instruction and the html is the root element.

So here are my questions:

Should the <html> remain on that second line?
If so, am I right in the explanation?
If not, can you tell me why?
What is the affect of having the line vs. not having the line?

Thank you all!