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After the usual state of a person or vehicle
pressure over the manholecover will
produce electricityand store down to emitting a
warning to play better lighting at night.
Safty cover - in the maintenance of the pipeline's construction,
has become an invisible killer,
when it opens, it is very easy to become a trap that many people
would have been invisible injury."Protector" of manhole cover
is such a simple design, when you
open the covers, pulled support from the covers form a striking