长期影响汇率的主要因素有
A、相对价格水平
B、关税和限额
C、进口与出口需求
D、生产率

单项选择题Which one uses the electrical property of carbon-carbon composites? A、Use carbon-carbon composite as power cables B、Use carbon-carbon composites as insulators C、Use carbon-carbon composites as monitors D、Use carbon-carbon composites as sensors.

单项选择题排气门在活塞位于 开启。A. 作功行程之前B. 作功行程将要结束时C. 进气行程开始前D. 进气行程开始后