新概念的问题:单复数时态

题目

新概念的问题:单复数\时态
新概念第三册:中有一句话:people who work in offices are frequently referred to as white-collar workers for the simple reason that they usually wear (a collar and tie) to go to work.这里为什么用a collar and tie 而不用collars and ties?
an american team explored a temple which (stands) in an ancient city on the promontory of ayia irini.这里stands 为什么不用stood?
回复sgdgzsg 同一段：they had large rooms with beautifully decorated walls.这个也是一直在那,为什么就不用一般时?

答案

我感觉they是虚指,不是复数的概念.我原来老爱用he or she如何如何,我的英语老师（洋人）就告诉我,我们都用they如何如何,不用he or she.
它一直在那,一般时
mother's day中mother是指群体,所以不是mothers'
第二个：我认为temple是直到探险队发现它的时候还在stand那,但是large room那个还是直到探险队发现时还是完好如初的吗?我猜是不是这个原因