青风藤碱与乌头碱的镇痛作用部位在（）
A、中枢神经系统
B、心血管系统
C、内分泌系统
D、外周神经系统
E、以上均非
参考答案：A
阅读下面语言材料，完成下面五个句子。
1. You can't talk to the bus driver when __________.
2. Mr. and Mrs. Biggs have to pay _________ for 2 nights.
3. You have to leave your expensive things in _________ in the hotel.
4. ________ people in the store today can meet Yao Ming.
5. Today skaters should go to the local _________.
生态平衡是一种 （ ）
A．永久的平衡
B．动植物数量相等的平衡
C．动植物数量保持不变的平衡
D．动态平衡
