凡有连续____次或_____次以上的室性早博发生时，临床称为室性心动过速。
参考答案：3；3
Of all the sports shoes, John bought _____ pair. Then he had some money for socks. [ ]
A. a cheaper
B. the most wonderful
C. the least expensive
D. an expensive
200-250km/h的线路圆曲线正矢差经常保养标准为（）mm。
A.1
B.2
C.3
D.4
