U波增高,可见于()
A.低血钙
B.低血钾
C.高血压
D.冠心病
E.高血钠
参考答案:B
People think "SOS" is the simplest and common _____ to make, in time of danger or disaster. [ ]
A. mark
B. sign
C. signal
D. remark
与其他产业相比,零售商业具有哪些特点?