The main concern for the Rome will be that the city of Rome could run out of grain bought from across the sea. Thus first option is correct.
A port can be defined as any area or harbor that can provide shelter to various boats and vessels and can allow the period or constant transportation of the ships from one area to the other.
The biggest concern for the Rome is the for shortage of the grains as grains are main source of the food. Much quantity of the grains are imported from the other countries.
The imports of the grain is done from the Africa and Egypt. With the ports being blocked will affect the diet of the Roman people and it will lead to the supply crises.
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