常用的机械传动有那几种？
参考答案：
有皮带、链条、齿轮三种。
硬度可分为（）和（）。
The kinked demand model assumes that below the current price, the demand curve becomes:（）
A. less elastic because competitors will not decrease their prices.
B. more elastic because competitors will not decrease their prices.
C. less elastic because competitors will decrease their prices.
