not one in a hundredchildren exposed to the disease()foung to developedAhas been Bbeing答案是A，为什么？

not one in a hundredchildren exposed to the disease()foung to developedAhas been Bbeing答案是A，为什么？
not one in a hundredchildren exposed to the disease()foung to developedAhas been Bbeing
答案是A，为什么？

not one in a hundredchildren exposed to the disease()foung to developedAhas been Bbeing答案是A，为什么？
100个接触过该疾病的儿童中没有发现一个儿童得了这种病.
主语是one ,所以后边用has been

B

我不知道原因，我只知怎样说才对
has been found to develop ...
being found developing ...

A 主语是not one in a hundred,谓语用单数，中间的exposed to the disease是定语