The situation is messy so I'll avoid details. I absolutely must do one module this February that is listed as 'level 3' at the Open University without formally taking the prerequisites. I have to teach myself the required mathematics, in two months, to give myself a decent chance of passing. If your only concern is to get the highest mark, which of the following do you choose? Imagine that you're completed your first year, been put in stasis in year 2, and awaken at the start of year 3 knowing none of the year 2 material. Electromagnetism: http://www3.open.ac.uk/study/undergraduate/course/smt359.htm The Quantum World: http://www3.open.ac.uk/study/undergraduate/course/sm358.htm The Relativistic Universe: http://www3.open.ac.uk/study/undergraduate/course/s383.htm I'll spare you my opinion since I don't know what I don't know.