There is a lot of spirogyra floating in this pond.

In this chemical reaction, hydration plays an important role.

This area is rich in subterranean rivers, which serve as a source of groundwater.

He is undergoing training for extravehicular activity.

He engaged in an extravehicular activity from the spaceship.

He is a foreigner, but he can speak Japanese fluently.

I have been to Outer Mongolia.

Coitus interruptus is one method of contraception, but it is not completely reliable.

This book explains in detail about the use of foreign words.

This sentence contains kanji not approved for regular use.