求问两项平行结构中to的省略有什么要求么

frank894848955

Unlike the original National Museum of Science and Technology in Italy, where the models are encased in glass or operated only by staff members, the Virtual Leonardo Project, an online version of the museum, encourages visitors to “touch” each exhibit, which thereby activates the animated functions of the piece.

A. exhibit, which thereby activates
B. exhibit, in turn an activation of
C. exhibit, and it will activate
D. exhibit and thereby activate
E. exhibit which, as a result, activates

乍一看d选项绝对不平行，看完答案才知道 encourage sb to do sth and do sth中间把to省了。我就疑问了to到底什么时侯能省什么时侯能不省？

wyx85

这个应该是一个logical predication，是先touch了，然后（thereby）才激活，所以要用and链接

cdbgin009

以省略后是否存在歧义为标准；这里因为encourages是单数，activate是复数，而前面复数动词只有touch，所以activate必与touch平行；省略to但是没有歧义