"because" does not quite work here. Also, I don't understand what you mean by "longest" form. Ignoring those issues, the normal phrasing would be "...
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Mickey Mouse 82411- Can railway systems opened by itself ? used active instead of passive form?!The system opened itn 1863. That is correct. It did not of, course, open by itself.
Mickey Mouse 8241 If we use "The London underground is the oldest system because it was opened in 1863."But we shouldn't. It's not natural.