Final answer:
Sudan is potentially at risk of locust swarms spreading west from Ethiopia, due to its geographical proximity and prevailing wind patterns.
Step-by-step explanation:
The country that could see swarms if they spread west from Ethiopia and was unaffected by locusts in September 2020 could potentially be Sudan. Considering the geographical proximity to Ethiopia, Sudan lies directly to the west and could be at risk if locust swarms migrate in that direction. The movement of locust swarms largely depends on the wind patterns and climate conditions, which could drive them towards neighboring countries.