题干
— ______ is the Changjiang River in China, do you know?
— Yes, it's about 6,380 kilometers long.
A：How many
B：How wide
C：How long
D：How much
答案(点此获取答案解析）
C
— ______ is the Changjiang River in China, do you know?
— Yes, it's about 6,380 kilometers long.
A：How many
B：How wide
C：How long
D：How much
），由于衰变它放出一个粒子，此粒子的径迹与反冲核的径迹是两个相外切的圆，大圆与小圆的直径之比为42∶1，如图所示。那么氡核的衰变方程应是下列方程的哪一个