左旋多巴对吩噻嗪类药物引起的帕金森综合征无效。
参考答案：对
____ we get on well with a number of people , we are usually friends with only a very few．
A．As
B．Once
C．Before
D．While
柴油机排气管冒蓝烟的原因是（）
A、机油过多
B、缸套磨损严重
C、气门调整不当
