Does a B grade in Year 10 5.3 maths enable a student to choose Prelim Maths (2 Unit) and Prelim Maths Extension 1 (3 Unit) in Year 11?
The Board of Studies has a list of Band descriptors on this webpage:
A10, A9, B8, B7, C6, C5, D4, D3 and E2
I think a C/D grade in Year 10 Maths 5.3, would mean you could do probably 2 Unit Maths only.
An A/B grade in Year 10 Maths 5.3 , could let you do 2 Unit/3 Unit math in Year 11.
If a student is in Year 10 Maths 5.2 and get an A grade, they can do 2 Unit Math. Your options are more limited if you take level 5.2 maths.