Hello every body , I have some questions about mikrotik RB1200

1- I would like about the Load Balance mechanism that Mikrotik use ie : what determines which traffic goes to which internet connection ( let say ISP1 : 10 Mb , ISP2: 8 Mb ) so how can I know which traffic will use ISP1 and which one will use ISP2 .

2- If I have one internet connection from an ISP , If I didn't use Radius to limit each user , will one user hug bandwidth from others .

3- can mikrotik do a link-bonding ie ( ISP1 + ISP2 = 10+8 = 18 Mb ) ????????