He is deeply studying the concept of hypostasis in theology.

This problem is just the tip of the iceberg.

Mr. Kagaku is my best friend.

The inner shell of this shellfish is very hard.

The inner enclosure of this castle is very sturdy.

The inner enclosure of this castle was very strong, and it was an important defense line to prevent enemy invasions.

He was observing the inner shell of the clam.

There is no ergative in Japanese.

My apartment is a five-story building.

He was standing on the seashore, staring at the distant horizon.