题干
The red-crowned crane is one of _______ in the world.
A：a rare animal
B：the rare animal
C：the rarest animals
D：the rarest
答案(点此获取答案解析）
C
The red-crowned crane is one of _______ in the world.
A：a rare animal
B：the rare animal
C：the rarest animals
D：the rarest
，动量的大小为
。如果一个静止的放射性元素的原子核在发生γ衰变时只发出一个γ光子，则衰变后的原子核是