most often only chosen 是什么结构（是否少了动词be）

问题描述

Private daycare or nannies are uncommon in Germany, and most often only chosen if government-funded or church-funded daycare is not available.

请问，句中 most often only chosen 是什么结构？可否加上动词 are，变成Private daycare or nannies are uncommon in Germany, and most often only are chosen if government-funded or church-funded daycare is not available.谢谢老师。

老师答疑

曹老师：

Private daycare or nannies are uncommon in Germany, and most often only chosen。。。

主句主语带了两个谓语：are uncomman和are chosen。第二个are承前省略。但第一个谓语是系表结构，第二个谓语是被动语态，两个be的性质不同。一般情况下不同性质的be不宜省略。因此本句and后最好表示出被动语态的are。most often和only分别为频度状语和强调性状语。

陈老师：

同意曹老师