Which idea did Ptolemy's model use to explain why the planets appeared to move backward as they moved in their orbits? The planets spun in epicycles. The planets rotated on their axes. The planets revolved around the Sun. The planets were made of different materials.

The planets spun in epicycles.

Explanation:

The planets were not simply attached to a mystical sphere (“deferent”) but they were actually attached to a mini-sphere (“epicycle”) which rotated on the larger one.

the simple machine has three main features. they are:

fulcrum is the center point or pivot point of the machine. effort is input force/ applied force. load is external force/ output.

the keisha 's machine labels are

x : load

y: fulcrum

z: lever

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).