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

[Q]: Lead sulfate is the white solid that forms on corroded battery terminals.
[A]: What is the white solid that forms on corroded battery terminals?


[Q]: Ribosomes are the only organelles that prokaryotic cells have.
[A]: What are the only organelles that prokaryotic cells have?


[Q]: Like all chordates, vertebrates are animals with four defining traits, at least during embryonic stage.
[A]:
Like all chordates, vertebrates are animals with four defining traits, at least during which stage?