What is the extension of this file?

Jikako is my best friend.

Namiko is my best friend.

Yukiko is my best friend.

Fumiko is my best friend.

Mikiko is my best friend.

This mochi is filled with plenty of delicious adzuki bean paste.

The adult son who still lives at home is causing trouble for his parents.

He picked up the short sword and began to practice.

This semiconductor material has the ability to generate excitons.