While answering this question , you can speak about your 
recent programs or achievements that you have done. You say 
about your program and how you developed this program.
Critical Part May be:
1.Coordinating with users.
2.During development of program.
3.Single hand job.
4.Anything that you think that you have done it for first 
time although it has been already developed or done by 
someone else.

My advise to you that never underestimate yourself and your 
achievements.
What you think is the critical is the critical in the 
project.