There is only one quiz at a time allowed. The reasons for this are so that you can take what you have learned from getting the first quiz put online and apply it to any subsequent quizzes, and so that everyone with a submitted quiz gets a fair shake at having their quiz looked at.
The only exception to this would be if you have a quiz that was once online pulled off for some reason. Then it could be submitted for consideration at the same time as a new quiz.
"To insult someone we call him 'bestial'. For deliberate cruelty and nature, 'human' might be the greater insult." - Isaac Asimov