find sb do/doing sth 变成被动的时候也不用加to
加to的是感官或使役动词
把这句话补充完整就是
anyone who was/is found trying to take petrol on board trains would be stopped.
结构是这样的
主句为 anyone would be stopped
然后anyone后面跟了一个过去分词做后置定语,补充完整就是定语从句.从句中是被动语态,find sb doing sth--find anyone trying to take petrol那你变成被动的时候不是 anyone who is found trying.
至于你说的为什么不用being found to try to take因为你是发现的时候正在携带汽油, 所以要用find sb doing sth 而不是 who was/is being found正在被发现 陈述一个事实,不用正在进行时
明白不?