"In the 1960s"为什么1960后要加S?

In the 1960s为什么1960后要加S? in the 1960's 与 in the 1960s 区别 为什么in the 1860s后面要加s? IN 1960S 还是IN THE 1960S in 1960's 和in the 1960s的区别 the incident took place in the ()1 1960.2 1960's.31960' .41960s.请选择答案及为什么 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? There is ( ) s in the word bus.括号里填啥,为什么 The policemen are in uniform为什么uniform不加s in poets of the 1960's是什么意思 who's the boy in blue?为什么要用inwho's the boy _ blue?为什么要用in in the cat,s In the stationary’s 为什么which produced were drawn 是错的?The car (produced)in Germany in the 1960s looks old now.Some pictures(drawn)by the Africans. 为什么What's the weather like in London in autumn?有两个 in the story happened _______________ A.in the 1940 B.in the 1940s C.in 1940 D.in the 1940s'为什么选B,1940后面为什么要加S,能不能说明下为什么? The cloud come from the water in the rivercome 为什么不加s不是第三人称吗 in the in the 1720's呢?