in 1840s 和 in the 1840s 哪个表达正确?如果都正确,有什么区别?

in 1900s 和 in the 1900s那个对? in 1960's 和in the 1960s的区别 in 1720s和in the 1720s的区别 in the 1980s,in the 1980's和in 1980s的区别 in the 19th 和in the 1980's in the 1990s,in the 1990's和in 1990的区别 in 1990 和 in the 1990s的区别 in the 1940's和in the1940s一样吗? in the cat,s In the stationary’s in the in the 1720's呢? in 1840s 和 in the 1840s 哪个表达正确?如果都正确,有什么区别? In the 1990S 和 In 1990s 和In 1990's 还有什么,怎么区分这几组词? in the 1930s和 in the 1930's有什么区别 in the 1990s和in the 1990's的区别 in the 1900's 和 in the 1900s的区别? in the 1980s和in the 1980's是不是都对的?有差别马? in the 1940s和in the 1940＇s的区别