What controls when Shrader valves open and close?

What controls when Shrader valves open and close?
 
  A) They open when they are backseat cracked and close when they are backseated.
  B) They open every time the unit starts up and close immediately upon shutdown.
  C) They open and close when hoses with depressors are connected and disconnected to them.
  D) They open and close by a wireless Bluetooth signal.

 Q. 2

Which of the following is defined by UL as a device that trips when a fault current to ground is 6mA or more?
 
  a. Class A
  b. Class B
  c. Class H
  d. Class R

 Q. 3

Which method enables ultraviolet (UV) lamps to be able to kill the maximum number of microbes in a duct
  system?
 
  a. Install UV lamps in the airstream ahead of an EAC.
  b. Constantly bathe the evaporator coil with UV light.
  c. Cycle the UV lamps on and off with the furnace blower.
  d. Install UV lamps in the return air duct airstream.