Somebody at quizilla says:
You are a GRAMMAR GOD!
If your mission in life is not already to preserve the English tongue, it should be. Congratulations and thank you!
How grammatically sound are you? brought to you by Quizilla

Based on the frequency of Grammar god scores visible via blogdex, a perfect score is not required. It’s also possible that one or more questions had more than one correct answer (in fact, one of them had to have had more than one correct answer, which gives the prescriptive morons a false sense of correctness).