The expantion of (a+b)^6 is ________ (^ is Power)
a^6+5a^6b+20a^3b^2+10a^2b^3+15a^5b^4+8ab^5+b^6+0a^1+0b^6
a^6-5a^6b+20a^3b^2-10a^2b^3+15a^5b^4-8ab^5+b^6
a^6+5a^5b+10a^4b^3+10a^3b^4+5ab^5+b^6
a^6+6a^5b+15a^4b^2+20a^3b^3+15a^2b^4+6ab^5+b^6