介质的绝缘电阻随温度升高而减少,金属材料的电阻随温度升高而增加。()
参考答案:对
These plastic flowers look so ________ that many people think they are real.[ ]
A.beautiful
B.natural
C.artificial
D.similar
麻黄碱是从哪种原植物中提取的()。
A.罂粟
B.大麻
C.麻黄草
D.古柯