题目内容
Once harm is _________ to the eco-system, all species will _________, including man himself．
[ ]
A．made; be in danger
B．done; be dangerous
C．caused; be endangered
D．done; be in danger
答案：D
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Once harm ______ to the environment, it takes years to have the system recovered.
| A．does | B．is done | C．will be done | D．be done |