Tricky CPL Air Law question.

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I'm preparing for an exam on Friday and came across the following question.

Any flight within an ADIZ will always be exempt from the 'general requirements' for such operations if -

a) the true air speed is below 120 kt
b) the flight does not proceed beyond 5 nm of the departure point
c) the flight is conducted in CTA
d) the flight originates from an aerodrome within the ADIZ

I chose D which was wrong, that only leaves B as being the most correct answer however.. AIP ENR 1.12-1 1.1.4.b states that the flight may remain within 10NM of the point of departure. What is the reasoning behind answer b ? What if I decide to proceed beyond 5nm and stay within 10nm...

Thanks in advance.

btw.. Air Law is the most boring CPL subject so far.