An analyst does research about the basic theories of the term structure. According to liquidity preference theory, the term structure of interest rates is least likely determined by:（）

A. expectations about future interest rates.

B. a yield premium for interest rate risk.

C. preference for particular maturity range.

列车运行中碰撞轻型车辆、小车、（）、防护栅栏等设备设施或钢轨、道砟、轨枕、道口铺面板即算事故。