instruction:
Given a scientific passage and an answer, generate a question for the given answer.
question:
Passage: Hydraulic car lifts also use fluid to transmit pressure and increase force. The lifts are used to raise cars, which are very heavy, so mechanics can work on them from underneath. Controls in airplanes use fluids to transmit pressure and increase force so a flick of a switch can raise or lower heavy landing gear. To see animations of hydraulic systems such as these, go to URLs:. Answer: hydraulic systems
answer:
What kind of systems use fluid to transmit pressure and increase force?

question:
Passage: Most gemstones are not used exactly as they are found in nature. Usually, gems are cut and polished. Figure below shows an uncut piece of ruby and a ruby that has been cut and polished. The way a mineral splits along a surface allows it to be cut to produce smooth surfaces. Notice that the cut and polished ruby sparkles more. Gems sparkle because light bounces back when it hits them. These gems are cut so that the most amount of light possible bounces back. Other gemstones, such as turquoise, are opaque, which means light does not pass through them. These gems are not cut in the same way. Answer: opaque
answer:
What are gemstones known as when light cannot pass through them?

question:
Passage: Bone marrow is a soft connective tissue that produces blood cells. It is found inside the pores of spongy bone. Answer: bone marrow
answer:
What is found inside the pores of spongy bone?