Step 1: Define an inland seaport. An inland port is a port on an inland waterway, such as a river or lake, which is connected to the sea by that waterway.
Step 2: Analyze the options.
Kolkata is a riverine port on the Hooghly River, about 128 km from the sea.
Manchester is connected to the sea by the Manchester Ship Canal.
Memphis (USA) is a major port on the Mississippi River.
Athens, Greece, is on the coast, but its main port, Piraeus, is directly on the Saronic Gulf of the Aegean Sea. It is a coastal port, not an inland port.
Step 3: Identify the one that is not an inland port. Athens (via its port Piraeus) is a coastal seaport.