Final answer:
The correct answer is 'before,' as it correctly conveys that guests must be connected to the primary lanyard prior to entering through the safety gate.
Step-by-step explanation:
The correct word to fill in the blank in the sentence "Guests must be connected to the primary lanyard before being allowed through the safety gate." is option a) before. This is because the sentence indicates a sequence of events where one action (being connected to the primary lanyard) is required to happen prior to another action (being allowed through the safety gate). The word before is used to show that one event must occur earlier in time than another.