Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
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Question: Cancer occurs most often in adults over fifty age.

Answer: Cancer occurs most often in adults over what age?


Question: Toxins is contained in the skin of brightly colored poison dart frogs.

Answer: What is contained in the skin of brightly colored poison dart frogs?


Question: Like all chordates, vertebrates are animals with four defining traits, at least during embryonic stage.

Answer:
Like all chordates, vertebrates are animals with four defining traits, at least during which stage?