填空题

It is bard to track the blue whale，______(它现在被列为濒危物种)．

【参考答案】

which is now listed as an endangered species

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填空题

B

单项选择题

Compared with genetic engineering of food crops, genetic engineering of trees______.

A．began much later
B．has developed more slowly
C．is less useful
D．is less controversial

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