Think of a MOSFET in place of the light switch: the switch itself is the "gate", the "source" is the power coming into the house, and the "drain" is the light bulb.
(the power; coming; into the house) (the "drain; is; the light bulb) (the "source; is; the power coming into the house) Context(the " source is,List([81, 96))):(the switch; is; the "gate)
the " source is,List([81, 96))
the power the "drain the "source the switch
coming is is is
into the house
the light bulb
the power coming into the house
the "gate