to 后面可接句子吗？

xixiokok

In order to design policies that aim to change commuting practices it is, however,necessary to have acquired a good understanding of the trips in question and their determinants.  
9 f4 n' w5 S0 K2 o- l! T
- W5 W: A# l( F% h这句话里，necessary to 后面为什么可以接 have acquired a ...句子？
3 f* C5 F8 G" N

江南一屁

9 f6 D; q/ A; m" B7 a+ I% Y没有接句子
) n8 L, c" S0 f# j! Eit is necessary to have done sth.
: C% B2 c+ b+ G) d. P接了个完成时的动宾结构

. r( s- R. ]: F+ v你可以对比一下下面两句的含义
it's necessary to acquire this.
有必要（现在或以后）去获取这个
it's necessary to have acquired this.
8 w( |6 F; o/ S. n5 i6 l+ y% u  @有必要目前已经获取了这个（具有这个是有必要的）
7 f& Y, E* t4 A
: F* r9 |" h* u1 G