He entered the marathon.

Research on retroviruses is greatly contributing to the advancement of medicine.

He decided to focus on the exam.

Tetrose is a monosaccharide with four carbon atoms.

Triose is a type of monosaccharide.

I want to go to Iturup.

He tried to imitate the crowing of a rooster.

I bought a new top.

An albatross is a bird with long wings.

Tetracosane is one of the important compounds in organic chemistry.