杨鹏长难句gmat 040， have had问题求解

CCCXL

040：Virgin-soil epidemics are those in whichthe populations at risk have had no previous contact with the diseases thatstrike them and are therefore immunologically almost defenseless.
关于have had 连用觉得好别扭，楼主英语基本功不太好。。
把have去掉 直接用at risk had no previous contact with。。。 不是挺好的吗，had过去式体现是过去的接触，
这里为什么要用have had呢。。有什么特别的意思？
请各位大佬指教，
btw，背诵杨鹏长难句真的大有裨益，大家一起坚持！

Fiona09

have no previous contact with ... 是指之前没接触过的。。。，这里是现在完成时的用法，have+动词的过去分词， 所以就是have had no previous contact with...

zoeyyoona

我认为have had done是和are 构成动作上的先后顺序。

追星少女吸氧

have had是现在完成时的用法哈，如果用had的话就变成一般过去时了，但句子中并没有明确指明发生在过去的时间状语；另外，have是跟后面的are并列的。

kluivert

Virgin-soil epidemics are those in which the populations at risk have had no previous contact with the diseases (that strike them) and are therefore immunologically almost defenseless.

表示 有/没有 xxx经历用完成时最简洁经济的表达方式啊
have never been to the States..... 你用did not 表达的意思完全不一样了...之是表示没去美国，但也许你曾经去过，只是这次didn't go
I've been to the states a million times ,but i didn't go last summer
have never tried sth
have seen that movie