Ku China, kumene ndalama zogwirira ntchito zikukwera komanso kuti anthu akusowa, maloboti ayamba kugwiritsidwa ntchito kwambiri m'madera osiyanasiyana, ndipo ogwira ntchito omwe amalowetsa mizere yopangira ma valve ndi maloboti amavomerezedwanso m'mafakitale ambiri odziwika bwino a valve. Fakitale yodziwika bwino ya ma valve ku ...
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