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？
