处于技术生命周期第二阶段的是（）
A.创新阶段
B.成长阶段
C.成熟阶段
D.衰退阶段
参考答案：C
－The temple looks very old.
－You are right. It’s said that it_______more than 300 years ago.
A．took apart
B．came into being
C．went through
D．built up
大量处在量子数n=3的激发态的氢原子向低能级跃迁时，能发出的谱线条数为______。
A．6 B．5C．4 D．3
