题目

 The subway was crowded with passengers going home from market, most of _____ carrying heavy bags and baskets full of fruit and vegetables they had bought there. A. whom             B. them             C. who              D. which 答案：B单缸四冲程内燃机在工作过程中，将机械能转化为内能的是（ ）A．吸气冲程B．压缩冲程C．做功冲程D．排气冲程