"which valve is an example of a special scuba valve that allows use of a redundant regulator with a single cylinder"

The   Y  valve alllow  the  is of  redundant  regulator   with  a    single  cylinder.  This  y  valve  is  a  chemical  and  corrosion  resistance  valve  which  is  designed  to  provide  flexibility  onboard  waste  management  by  diverting  waste  either  in  onboard   holding  tank  or  directly  to    overboard  holding  tank.

Three reasons of the deaths of native americans: new illnesses that their immune systems couldn't cope with. genocides so the settlers could have the good land.starvation from lack of rations and poor infertile land on resevations

Ao, bo, ab, bahope these