Edwin constructed a model of the Sun, Earth and Moon system and placed it on a table to show his class. He designed it so that the Moon can move around the Earth. When Edwin shines a light on the Earth, the Moon casts a shadow on the Earth. This represents a solar eclipse.

a model of the Sun, Earth, and Moon

Edwin rotates the Moon around the Earth to show a full month. After one full revolution around the Earth, the Moon casts a shadow on the Earth again. Another student states that if this models the Sun, Earth and Moon correctly, then a solar eclipse would happen once a month.

Edwin found out a solar eclipse happens about once every 18 months. How should Edwin improve his model to better represent how often eclipses occur?
A.
He should make the Sun a large, round object.
B.
He should make both the Earth and the Moon spin on their tilted axes.
C.
He should make the Moon orbit Earth at an angle to the table, and not parallel.
D.
He should make the Earth orbit around the Sun.