What is the genus in the following definition? The horizon is the line of separation between the sky and the earth.

A) horizon
B) sky
C) line of separation
D) earth
E) There is no genus.

"Genus" refers to the general category or class to which a specific thing belongs. In this definition, "line of separation" is the genus because it is the overarching category to which the specific thing, the horizon, belongs. The horizon is a specific example of a line of separation between two things, which could include other examples such as the horizon of a lake or the horizon between two mountains.