Final answer:
Nelson Mandela joined the African National Congress (ANC) before he was sent to Robben Island; he later became South Africa's president and a Nobel Peace Prize laureate after his release.
Step-by-step explanation:
Among the given options, the event that happened before Nelson Mandela was sent to Robben Island is Option 4: He joined the African National Congress (ANC). Before his imprisonment, Nelson Mandela served as a lawyer in Johannesburg, becoming actively involved in the anti-apartheid movement and joining the ANC. His work in the ANC led to his arrest and subsequent 27-year imprisonment, of which he spent 18 years on Robben Island.
His election as President of South Africa and his winning of the Nobel Peace Prize both occurred after his release from prison. He was elected president in the historic 1994 elections and awarded the Nobel Peace Prize in 1993, in recognition of his efforts to dismantle the apartheid system in partnership with then South African President F.W. de Klerk.