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

[Q]: Passage: In the solar system, the planets orbit around the Sun. The Sun and each of the planets of our solar system are round. Earth is the third planet from the Sun. It is one of the inner planets. Jupiter is an outer planet. It is the largest planet in the solar system at about 1,000 times the size of Earth. The Sun is about 1,000 times bigger than Jupiter! ( Figure below ). Answer: the sun
[A]: What do the planets orbit around in the solar system?

[Q]: Passage: Biofuels are useful because they are liquid. Biofuels can go into a gas tank unlike many other types of alternative energy. Answer: liquid
[A]: What form do biofuels take that makes them very useful?

[Q]: Passage: When you use a machine, you apply force to the machine. This force is called the input force. The machine, in turn, applies force to an object. This force is called the output force. The output force may or may not be the same as the input force. The force you apply to the machine is applied over a given distance, called the input distance. The force applied by the machine to the object is also applied over a distance, called the output distance. The output distance may or may not be the same as the input distance. Answer: output force
[A]:
What do you call the force a machine applies to an object?