Student:
You're asking us to design a circuit in Quartus using active-low 
signals.  You said in class that Quartus doesn't understand 
active-low. <br> <br> 

Dr. S.: Quartus does not NEED to understand active-low signals. <br> <br>

Student: 
I'm not sure what I'm missing here.  If you could get back to me 
when you have the chance, I'd appreciate it.  Thanks for your time.
<br> <br>

Dr. S.: Make a simple circuit (one NAND gate) with at least one active-low
input or output. Write the equation.  Make a truth table.  Convert the truth
table to a voltage table.  Draw the circuit exactly like you did on paper 
in Quartus.  Simulate the circuit.  Note that the Quartus simulation output 
(which is a VOLTAGE simulation output) exactly matches your voltage table output.  
This demonstrates that Quartus does not care about activation levels.
<br> <br>

Hope this helped. <br> <br>

All the best,<br>
Dr. Schwartz