[@Nikki Moonlight]
If you can't do the minimum amount of sentences then either make them shorter each time or at least go to about seven lines. Some people do really long sentences, like me, so that's why there's also an option of doing a certain amount of lines.
Being over-descriptive can also help you. The problem is that sometimes things can repeat or get boring from reading such a long description of one thing. Try not to do too much of that. Maybe do different things like describing your surroundings, how they're effecting your character, what the character senses, etc. to keep the length up.

Oh, and this post is already six sentences. There's your example.