单项选择题

A．If they don’t involve any risks.
B．If they produce predictable side effects.
C．When the urgent need for them arises.
D．When tests show that they are relatively safe.
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单项选择题
A．Mating habits of squid and octopus.B．The evolution of certain forms of sea life.C．The study of marine shells.D．Survival skills of sea creatures.
A．Mating habits of squid and octopus.
B．The evolution of certain forms of sea life.
C．The study of marine shells.
D．Survival skills of sea creatures.
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