My father is a doctor.

In the old days, people used to consider milk as an important source of nutrition.

He studies hard every day.

He started a business without a plan, forgetting the lesson of 'peach and chestnut seeds take three years to bear fruit, persimmons eight years.'

Crux is one of the constellations in the southern hemisphere.

He gripped the control stick and piloted the plane.

The 24-cell is one of the convex regular polytopes in four dimensions.

He found a regular dodecahedron-shaped spicy cod roe.

He made a model of a regular icosahedron.

Heavy hydrogen is one of the isotopes of hydrogen.