How often does the Earth orbit around the moon?

The correct answer is based on the understanding of the relationship between the Earth and the Moon. The Earth does not orbit the Moon; rather, the Moon orbits the Earth. This is a fundamental concept of our solar system's structure, where the Earth is the larger body that gravitationally attracts the Moon, causing it to revolve around the Earth. The Moon completes one orbit around the Earth approximately every 27.3 days, which is the length of a lunar month.

In contrast, the other options suggest frequencies of orbiting that do not align with the established astronomical understanding. The notion of the Earth orbiting the Moon, whether monthly, yearly, or biennially, is contrary to this gravitational relationship, reinforcing the clarity that it is indeed the Moon that completes an orbit around the Earth, not the other way around.