in the 1970s 的“s”表示什么?

in the 1970s 的“s”表示什么? in the 1970s；in 1970s；in 1970's；in the 1970's哪个对? 英语年代的表示?Our country changed a lot ____.A.in 1980s B.in 1980'sC.in the 1980s D.the 1980s in 1960's 和in the 1960s的区别 in 1980's 与 in the 1980's的区别 in 1720s和in the 1720s的区别 In the 90s 与In 90s 的区别 in the 1970s=in the 1970's还是=in 1970's in 1970s; in the 1970's ; in the 1970s'.那种对呀, in the 1980s,in the 1980's和in 1980s的区别 in 1950s 与in the 1950s有什么区别?in 1950s是表示1950----1959还是1940---1949?in the 1950s呢? from the 1990s in the 1990s的区别 in 1970、in the 1970、in the 1970‘s、in the 1970s有什么区别 in the cat,s In the stationary’s 有关英语年代表示法的问题!比如说在17世纪 到底是用 in the 1600's 还是 in the 1600s 英语年代表示方法in 1980's 、 in 1980s 、 in 1980的区别 英语中可以用’80s表示八十年代吗?in the '80s 这样可以吗？