He followed the footprints left on the snow.

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.

He was feeling loneliness.

He provided a detailed explanation to elucidate the issue.