反映色谱柱柱型特性的参数是（）
A.分配系数
B.分配比
C.相比
D.保留值
参考答案：C
各省公司网络维护部门要建立跨省集团客户传输专线的例行巡检维护制度，巡检周期重要客户每（）1次。
A.周
B.月
C.季度
Mr. Jenkins has been busy with his work these days and seldom _________ to come over to have a chat with me.
A．has he time
B．does he have time
C．hasn’t he time
D．doesn’t he have time
