皮带传动的主要缺点之一是（）

A.传动不平稳

B.传动比不稳定

C.传动效率很低

D.不能作变向传动

Why are the prices of mobile telephone services lower in China’s eastern coastal region a. The average disposable income is lower in the region. b. The GDP is higher in the region. c. The costs of operators are lower due to a greater number of users of mobile phone services in the region. d. The operators compete with each other in order to win over subscribers.