请教一个英语的语法问题RepliesshowthatcomparedwithotherAmericans,journalistsaremorelikelytoliveinupscaleneighborhoods,havemaids,ownMercedeses,andtradestocks,angtheyarelesslikelytogotochurch,dovolunteerwork,orput

　　请教一个英语的语法问题

　　RepliesshowthatcomparedwithotherAmericans,journalistsaremorelikelytoliveinupscaleneighborhoods,havemaids,ownMercedeses,andtradestocks,angtheyarelesslikelytogotochurch,dovolunteerwork,orputdownrootsinacommunity.

　　上面这个句子中“RepliesshowthatcomparedwithotherAmericans”里面的compared用了过去式,这是为什么,就算是过去式的话,不是应该有be动词吗,本人语法知识较为贫乏,希望讲解的人能讲得详细一点.