This hardened dirt is so hard, nothing can be planted.

A central vowel refers to a vowel where the position of the tongue is in the middle.

The central vowels in Japanese are 'a', 'e', 'o'.

It is said that this area used to be a mass grave.

The United Nations Environment Programme is providing solutions to global environmental problems.

My room is the quietest in the house.

He checked whether he remembered or not.

The parasympathetic nerves help our body to relax and conserve energy.

He was in a sickbed for a long time.

I decided to take a sick leave.