题目

After years of hard work, his efforts, which was quite a relief. A. made up                          B. paid off C. took on                              D. hold back 答案：B工业社会以来，不是造成物种灭绝的速度提高的原因是（　　）A．人类过渡开发利用生物资源B．滥捕滥杀C．建立自然保护区D．环境污染