in the 1940s和in the 1940＇s的区别

in the 1940's和in the1940s一样吗? in the 1940s和in the 1940＇s的区别 in the 19th 和in the 1980's in the 1980s,in the 1980's和in 1980s的区别 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 cat,s In the stationary’s in the 1940's in 1940s in the 1940s区别~ in the 1990s,in the 1990's和in 1990的区别 in the in the 1720's呢? in the1940's 和in the 1940s意思的区别 in 1990 和 in the 1990s的区别 in 1980/in 1980s / in the 1980 / in the 1980s / in the 1980's/in the 1980' in the 1940s 与in the 1940's的区别?为什么My brother served in the army in the 1940's.这一句子中要用in the 1940‘s而不用in the 1940s? in the 1920's和in the 1920s 有何区别么?the 1920's和in the 1920s 有何区别么? in the 1930s和 in the 1930's有什么区别