He is a good correspondent, always writing letters.

He is a very diligent person.

His diligence in his work was appreciated, and he was promoted.

He is an expert in ethology, and his research is highly regarded worldwide.

This ancient proverb, 'know the other side and yourself, and you will not be in danger in a hundred battles', teaches us the importance of understanding ourselves and others.

He is always joking around during class.

His irregular lifestyle is having a negative impact on his health.

The Calopteryx cornelia is a species endemic to Japan, and it has beautiful wings.

He is receiving countless blessings.

The indefinite article is a basic part of English grammar.