问题 选择题
在匀强磁场中有一个原来静止的碳14原子核,它放射出的粒子与反冲核的径迹是两个相内切的圆,如图所示.那么碳14的衰变方程为(  )

A.+

B.+

C.+

D.+

答案

答案:D

材料题

阅读材料:

       孙中山先生就任临时大总统后,有一位八十多岁的盐商,专程从外地赶到南京,想看一看大总统的风采。见面的时候,孙中山正准备和他握手,他已放下手杖,跪下去恭恭敬敬地行起了三跪九扣大礼。孙中山先生连忙拉他起来,请他坐下,亲切地和他谈话。从这一段文字中可以看出民国前后社会习俗有了哪些变化?这些变化说明了什么问题?

                                                                                                                                                             

                                                                                                                                                             

                                                                                                                                                             

                                                                                                                                                             

单项选择题