You are presented with the quiz "Running water is better able to dissolve oxygen and nutrients than what?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "running water is better able to dissolve oxygen and nutrients than standing water" and "if the water stands still and becomes stagnant, it can become a breeding ground for mosquitoes". 

So, what's the best answer to the question?


 

        stagnant water   