谁能帮我解释一下下面的句子，划线部分做什么成分，为什么要加TO？谢谢！

steve

At the time of the Mexican agrarian revolution, the most radical faction, that of Zapata and his followers, proposed a return to communal ownership of land, [U]to what had been a pre-Columbian form of ownership respected by the Spaniards.[/U]

steve

但问题是，如果是同位于的话，我觉得TO大课不必加，用WHAT也可以代替前面一堆东西。

yuandong

没错，是同位语。这题很搞

princess

to what…是to communal ownership of land,的同位语

vin0410

所以是to what…是to communal ownership of land,的同位语?
还是land的同位语?

tongxun

补充说明前面的to 。。。land。解释到底是to成什么样。

eastcreat

背一下此结构。
省略LAND，   应为 land to what had been....,做前面的同位语，起补充说明作用