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

[Q]: Respiratory acidosis is considered to be problematic because excess co2 in blood.
[A]: Why is respiratory acidosis considered to be problematic?

[Q]: Ionic compounds contain cations and anions rather than discrete neutral molecules.
[A]: Ionic compounds contain cations and anions rather than what?

[Q]: Vertebrata are characterized by the presence of backbone.
[A]:
Vertebrata are characterized by the presence of what?