This one goes with the multiple choice questions: 

https://www.youtube.com/watch?v=yIp4m_v9xGs&list=PL396FF0F0A43B5D68&index=4

This one is just interesting:

https://www.youtube.com/watch?v=x-387NMCR6w&list=PL396FF0F0A43B5D68&index=3