The correct answer is option 4: Fiords. Stalactites, stalagmites, and sink holes are all formed as a result of underground water action, but fiords are not.

Stalactites are icicle-like formations that hang from the ceilings of caves. They are formed when minerals in water seep through the cave roof and slowly deposit, creating a long, hanging column. Stalagmites, on the other hand, are formations that rise from the cave floor. They are formed when mineral-rich water drips from the ceiling and builds up over time, creating a tall, cone-shaped structure. Both stalactites and stalagmites are common in limestone caves.

Sinkholes are depressions or cavities that form on the Earth`s surface due to the dissolution of underground rocks by water. They occur when the ground is unable to support the weight above it, causing it to collapse. Sinkholes can vary in size and can be dangerous if they occur suddenly.

Fiords, on the other hand, are narrow, deep inlets or bays that are typically found in areas where glaciers have carved out valleys and then receded. They are not formed by underground water action but rather by the movement of glaciers.