Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Stringed instruments can help show the relationship between tension and frequencies in strings.
Stringed instruments can help show the relationship between tension and what in strings?

Chewing insects such as dragonflies and grasshoppers have two many sets of jaws.
Chewing insects such as dragonflies and grasshoppers have how many sets of jaws?

Autotrophs is another name for producers.
What is another name for producers?