SAT Question 109d5bbb: Boundaries answer and explanation

English - Boundaries - Punctuating Nonessential Element
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With some 16,000 in attendance, the Second World Black and African Festival of Arts and ______ or FESTAC ‘77, as the event was more commonly known—became the largest pan-African event on record. FESTAC drew people from around the world to Lagos, Nigeria, for a monthlong celebration of Black and African art, scholarship, and activism.
10
Difficulty:Hard
Which choice completes the text so that it conforms to the conventions of Standard English?