放射性原子核A经一系列α和β衰变变为原子核B．若B核内质子数比A核少8，中子数比A核少16．则发生β衰变的次数为 次．
4
By age 7 months, an infant most likely will develop which of the following motor skill
A. Walk with one hand held.B. Eat successfully with a spoon.C. Stand while holding onto furniture.D. Sit alone using the hands for support.
输卵管结核早期的表现（）.
A.管壁增厚
B.管腔狭窄甚至闭塞
C.黏膜破坏，管腔扩张
D.管壁僵直
E.输卵管发生钙化
