Which join type should you use?

Your network contains a System Center 2012 Configuration Manager environment.
You have the following query:
Select Name
from
SMS_R_System R
join SMS_R_User U
on R.LastLogonUserName = U.UserName

You need to ensure that all of the client computers are listed in the query results.
Which join type should you use?

A.
LEFT

B.
FULL

C.
INNER

D.
RIGHT