问题描述：
The conservation group said half the mammals that
have become extinct globally in the last 200 year have been Australian species.在that引导的定从中真正的动词是什么?是have become 还是have been.如果是其中一个那另一个在句中做什么成分?请高手指教下.
have become extinct globally in the last 200 year have been Australian species.在that引导的定从中真正的动词是什么?是have become 还是have been.如果是其中一个那另一个在句中做什么成分?请高手指教下.
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