Scientists also have no idea how long it will be before all wild animals in the cages . A

问题补充：

Scientists also have no idea how long it will be before all wild animals in the cages .

A. should be set free

B. will be set free

C. are set free

D. would be set free

答案：

A. should be set free

B. will be set free

C. are set free

D. would be set free

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