—_____ have you been to Beijing?

—Twice.[ ]

A. How much time        

B. How many times

C. How many time        

D. How much times

诊断冠心病心绞痛最常用的非创伤性检查方法是（）

A.休息时心电图

B.24小时动态心电图

C.心电图运动负荷试验

D.超声心动图

E.心脏CT检查