单选题 The toxin produced by certain marine snails contains various proteins, one of which, when injected into mice, made mice aged two weeks or younger fall asleep and made older mice run for hiding places.
When mice are suddenly seriously threatened, very young ones react by staying perfectly still, whereas older ones run away.
The facts stated above provide the strongest support for which of the following working hypotheses?

A、 The reaction of mice to sudden, serious threats is triggered by a chemical produced by the body, and this chemical is similar to the protein that was injected into the mice.
B、 The protein contained in snail toxin that was injected into the mice ordinarily has the primary function of protecting snails by inducing in those snails complete immobility.
C、 The protein that was injected into the mice would have made the mature mice fall asleep, too, if they had been injected with larger doses.
D、 Very young mice are as likely to be exposed to sudden serious threats as are older mice.
E、 (E) Very young mice are not developed enough to deal appropriately with even the stimuli that they are most likely to encounter.

【正确答案】 A

【答案解析】