Given a scientific passage and an answer, generate a question for the given answer.

Passage: David Remahl. Polygenic traits result in a distribution that resembles a bell-shaped curve . The creator of this work allows anyone to use it for any purpose including unrestricted redistribution, commercial use, and modification. Answer: bell-shaped
Polygenic traits result in a distribution that resembles a curve. what is the shape of the curve?

Passage: There are three types of mechanical waves. They differ in how they travel through a medium. The three types are transverse, longitudinal, and surface waves. All three types are described in detail below. Answer: three
How many types of mechanical waves are there?

Passage: Distillation is an effective method to separate mixtures comprised of two or more pure liquids. Distillation is a purification process in which the components of a liquid mixture are vaporized (transformed from liquid to gas) and then condensed (transformed from gas back to liquid) and isolated. In a simple distillation, a mixture is gradually heated. The solution with the lowest boiling point will change into a gas first. This gas, or vapor, then passes through a cooled tube (a condenser) where it condenses back into its liquid state. This condensed liquid is called the distillate. Figure below illustrates this. Answer: pure liquids
Distillation is an effective method to separate mixtures comprised of two or more what?