مطلوب على وحه السرعة

[memomando]

when must i wear a helmet?
is right because you are asking someone to give you information about a rule you must do

[Mr.Nashaat Elhamaki]

I think
When must you................... ) is possible
but
When must I...................) is better
So
in re write both of them are right
but
in Choose
I ) is the right answer (