in 1980/in 1980s / in the 1980 / in the 1980s / in the 1980's/in the 1980'

in 1980/in 1980s / in the 1980 / in the 1980s / in the 1980's/in the 1980' in 1980s or in the 1980sAs i said...which one is correct? I have served army___when I was__. A.in the 1980's,in the twenties B.in the 1980's,in my twenties在某人20岁, 到底是in the twenties还是 in my twenties?谢谢各位! in 1980's 与 in the 1980's的区别 in the 1980s,in the 1980's和in 1980s的区别 I was born in _____andI was born in ____and studied at this school ____.A in 1980; in the 1990B in the 1980；at the 1990sC in1980; at the 1990sD in 1980； in the 1990s我知道是选D,但是为什么呢?In 加年,不加介词吗?in the 1990s 为什 英语年代表示方法in 1980's 、 in 1980s 、 in 1980的区别 in the 1980s 与 in 1980的区别 Great changes happened in China in the 1980s翻译 in the 19th 和in the 1980's I went to collage in?and began to work in A.the 1980s;twenty B the 1980's ;my twenties I was in barber's chair 为什么介词用in I thank it's in your grandparents' that's exactly what i had in I's in the middle of China i miss one's in my life In fact there's nothing I cant I say:Give in,be thoroughly's