Which courses Alicia takes is fully determined if she takes Russian and which one of the following?

In the video she says that we know Russian and WH is in and G is out and we don't know anything more. I disagree, please explain why my logic is wrong. If you have R and WH then you know you cannot have S9 so you must have S3 so now you have R,WH,S3 and since we have R we cannot have J which means we have M so you have four. R, WH, S3, M. I would venture a guess that you will tell me I cannot assume that because we do not have s9 that we have s3. However, if we do not "assume" then would this answer be more of choose the best answer type question? How do I stop myself from falling into these traps of assumptions? Sometimes we are told to assume and other times we get them wrong when we do? Thanks for your help in advance!