Classify the below list of 10 songs by genre:

1. Hail Mary - Tupac
2. Juicy - The Notorious B.I.G.
3. Insane in the Brain - Cypress Hill
4. Can't Knock the Hustle - Jay Z
5. How's It Going Down - DMX
6. If I Ruled the World - Nas
7. O.P.P. - Naughty by Nature
8. It Was a Good Day - Ice Cube
9. C.R.E.A.M. - Wu-Tang Clan
10. Regulate - Warren G
 
The 10 songs listed are all rap songs.  Additionally, they were all released in the 1990's.