Option 1 -> Incorrect sequence - starts correctly but places consequences before the polluting action.
Option 2 -> Correct sequence - (A) introduces the refinery, (C) describes the pollution, (B) explains the harmful effects, (D) defines externalities.
Option 3 -> Incorrect sequence - begins with effects before introducing the source.
Option 4 -> Incorrect sequence - starts with pollution before introducing the refinery.
Hence, Option 2: (A), (C), (B), (D) -> The logical flow begins by introducing the oil refinery as the economic agent (A), then describes how its production process pollutes the river (C), followed by the harmful consequences of this pollution on well-being and organisms (B), and finally concludes with the economic definition that these uncompensated harmful effects are called negative externalities (D). This sequence follows a clear cause-and-effect progression from entity → action → consequence → conceptual definition. -> correct