Great changes have taken place since you left.这句话是个什么从句?省略了什

Great changes have taken place since you left.这句话是个什么从句?省略了什 many great changed have taken place since you left.这语法是对的吗? Great changes have taken place since liberation Great changes have taken place in my hometown since 1930. "Great changes have taken place in China since the introduct Great changes have taken place in my hometown since 1980 .为什 Many changes have taken place since Recently,great changes have taken place in my home town.这句话成 Great changes have taken place there. Great changes have taken place there Great changes have taken place ...in china Great changes have taken place in China.