He was playing by swinging the tree branch.

It is important to learn about the prevention and treatment of the human immunodeficiency virus.

It's difficult to handle this machine.

He continued to explain earnestly.

He is feeling solitude.

The human immunodeficiency virus destroys the immune system, causing the body to lose its ability to fight disease.

The human immunodeficiency virus destroys the immune system, making the body unable to fight disease.

Ogura Hyakunin Isshu is one of the classical literatures of Japan.

He said, 'If you want to shoot a man, first shoot his horse,' and began to solve the smaller problems first.

Zoonosis is a disease that spreads from animals to humans, or vice versa.