in the 1990s'还是in the 1990's

in the 1990s'还是in the 1990's in 1990s还是in the 1990s in early 1990s还是in the early 1900s? 是in the 1980's还是in 1980's in the 1950s 还是in 1950s IN 1960S 还是IN THE 1960S in the 1950s还是in 1950s from the 1990s in the 1990s的区别 in the 1990s 、 in 1991s 、 in the 1991s、 in 1990都有什么含义? 是in1980s还是in the 1980s in the cat,s in the 1970s