This phenomenon remains unexplained for scientists.

He is known as a person with learning.

Koushirou is my best friend.

Kou Sennen is my best friend.

The photoelectric effect is a phenomenon where a material emits electrons after absorbing light.

Photochemistry is a branch of science that studies how chemical reactions proceed under the influence of light.

We have a responsibility to protect the biodiversity of the Earth.

He runs in the park every day.

He raced in a marathon.

I am majoring in microbiology at university.