同一无性系的桉树人工林，密度太大，第一次抚育间伐时（疏伐），可选择（）
A.上层疏伐
B.下层疏伐
C.机械疏伐
D.综合疏伐
参考答案：C
— Why is the chemical plant closed?
— Because large quantities of waste water ______ into the Yangtze River.
A．has been released
B．is being released
C．was released
D．have been released
目前在欧洲旱地冰球开展较好的国家包括捷克、芬兰、瑞典和（）等国家。
A.挪威
B.瑞士
C.英国
D.法国
