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

[EX Q]: Saturated hydrocarbons hydrocarbons contain only single bonds between carbon atoms.
[EX A]: What hydrocarbons contain only single bonds between carbon atoms?

[EX Q]: The long, threadlike extensions of the nerve cell help transmit nerve impulses.
[EX A]: Which part of the nerve cell helps transmit nerve impulses?

[EX Q]: The innate immune system serves as a first responder to pathogenic threats that bypass natural physical and chemical barriers of the body.
[EX A]:
What serves as a first responder to pathogenic threats that bypass natural physical and chemical barriers of the body?