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

Example Input: Passage: A metallic bond is the force of attraction between a positive metal ion and the valence electrons that surround itboth its own valence electrons and those of other ions of the same metal. The ions and electrons form a lattice-like structure. Only metals, such as the copper pictured in the Figure below , form metallic bonds. Answer: metallic bond
Example Output: What is the force of attraction between a positive metal ion and valence electrons?

Example Input: Passage: Air movement takes place in the troposphere. This is the lowest layer of the atmosphere. Air moves because of differences in heating. These differences create convection currents and winds ( Figure below ). Answer: troposphere
Example Output: What is the lowest layer of the atmosphere called?

Example Input: Passage: Brass saxophone: Brass is an alloy of copper and zinc. It is softer than bronze and easier to shape. It's also very shiny. Notice the curved pieces in this shiny brass saxophone. Brass is used for shaping many other curved objects, such as doorknobs and plumbing fixtures. Stainless steel sink: Stainless steel is a type of steel that contains nickel and chromium in addition to carbon and iron. It is shiny, strong, and resistant to rusting. This makes it useful for sinks, eating utensils, and other objects that are exposed to water. "Gold" bracelet: Pure gold is relatively soft, so it is rarely used for jewelry. Most "gold" jewelry is actually made of an alloy of gold, copper and silver. Bronze statue: Bronze was the first alloy ever made. The earliest bronze dates back many thousands of years. Bronze is a mixture of copper and tin. Both copper and tin are relatively soft metals, but mixed together in bronze they are much harder. Bronze has been used for statues, coins, and other objects. Answer: brass
Example Output:
What alloy is made from copper and zinc?