Option 1 -> This sequence starts with Chernobyl (1986), but incorrectly places the Fall of Saigon (1975) at the end, which is chronologically wrong.
Option 2 -> This sequence is nearly reversed, starting with the most recent event (Russia's invasion in 2022) and ending with the oldest (Fall of Saigon in 1975).
Option 3 -> This sequence incorrectly places the European migrant crisis (2015) before Chernobyl (1986) and the Fall of Saigon (1975) before Russia's invasion.
Option 4 -> This correctly sequences the events: Fall of Saigon (1975), Chernobyl disaster (1986), European migrant crisis (2015), and Russia invades Ukraine (2022).
Hence, Option 4: (D), (A), (B), (C) -> The Fall of Saigon occurred in 1975, followed by the Chernobyl nuclear disaster in 1986, then the European migrant crisis peaked around 2015-2016, and finally Russia's invasion of Ukraine began in 2022 -> correct