根据句意和汉语提示，填写单词。

1. His brother is a _________(军人). He joined the army five years ago.

2. We must _________(面对) these problems and find ways to get over them.

3. The old man _________(将……视为) the poor boy as his own son.

4. ________ (除非) we work hard, we will hardly ever learn English well.

5. There is a popular saying in sports meeting, "________(友谊) first, competition second."

关于原子核外结构的叙述，错误的是

A．原子均由核及核外电子组成
B．电子沿一定轨道绕核旋转
C．核外电子具有不同壳层
D．K层最多容纳8个电子
E．K层电子半径最小