Turn the given fact into a question by a simple rearrangement of words. This typically involves replacing some part of the given fact with a WH word. For example, replacing the subject of the provided fact with the word "what" can form a valid question. Don't be creative! You just need to rearrange the words to turn the fact into a question - easy! Don't just randomly remove a word from the given fact to form a question. Remember that your question must evaluate scientific understanding. Pick a word or a phrase in the given fact to be the correct answer, then make the rest of the question. You can also form a question without any WH words. For example, "A radio converts electricity into?"

Fact: Receptors in the lining of the nose are used to find food.
Receptors in the lining of the nose are:?

Fact: plants are the major producers of ecosystems that make up the land.
What are the major produces of ecosystems that make up the land?

Fact: A switch is used to start the flow of electric charge in an electrical circuit.

A switch is used to start the what of electric charge in an electrical circuit?