In X-Men: Days of Future Past I see several things about absence of metal that I am a bit skeptical about.
For example, Magneto is being held under the Pentagon and there should be no metal whatsoever hundreds of meters around him. But how do they provide lighting and electricity to power the security and comm systems down there? It is 1973, were there technologies to deliver energy without using metal back then?
Another example were Trask's sentinels, made of "modern polymers", without metal. What about their CPUs and other computing hardware?
So, the the question is, were there technologies back in 1973 that would allow the creation of metal-less underground prison cell and giant robots?
EDIT1: as an additional question, maybe the details about the technology are mentioned somewhere in the universe?