Provisions like Rule 8 are best read by asking what mischief they are trying to prevent, and then checking whether each named body actually creates that mischief.
Testing each body against the mischief Rule 8 is meant to prevent shows that only membership of the Executive Committee creates the operational closeness the rule is targeting.
So, the correct answer is Executive Committee.
Professional conduct rules are drafted with deliberate precision, and the specific term chosen by the rule-maker often points directly to the answer. Looking at why Rule 8 uses the particular words it does helps settle this question.
The precise wording of Rule 8, naming the Executive Committee and nothing broader, shows that only membership of that specific body was meant to disqualify an advocate from appearing for or against the organisation.
Hence, the correct answer is Executive Committee.