Nitrogen dioxide is a cause of air pollution.

He commutes by two-wheeled vehicle.

Fujiko is my best friend.

His speech was a double negative, making it difficult to understand.

Nikaido-san is my best friend.

The Second International was established to protect the rights of workers.

Where will the second party be held?

Solving a quadratic equation is difficult.

He is really handsome, isn't he?

Binomial nomenclature plays an important role in biological taxonomy.