He was appointed as the chief executive officer of the company.

Infrared astronomy provides a new perspective on understanding the universe.

By regularly checking the key performance indicators, you can understand the performance of the company and devise improvement measures.

Functional analysis is a branch of mathematics that studies the properties of functions in infinite-dimensional spaces.

The Mesolithic is the era between the Paleolithic and the Neolithic.

The Riemann sum is a method for approximately calculating the integral of a function.

I stabbed the needle for the injection.

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

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

He left early to avoid the problem.