You'd better tell your friends the of smoking. [ ]
A. dangers
B. dangerous
C. dangered
A
如果半径分别为2cm和3cm的两圆外切,那么这两个圆的圆心距是[ ]
A.1cm
B.5cm
C.1cm或5cm
D.小于1cm或大于5cm
单环式保险绳如何使用?