Analog Electronics
Pinch-off voltage in a JFET is

 the gate to source voltage that gives zero drain current.
 the gate to source voltage that gives unity drain current.
 the drain voltage that gives zero drain current.
 the drain voltage that gives infinite drain current.

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Analog Electronics
Optocouplers combine

 SITs and BJTs.
 IGBTs and MOSFETs.
  Infrared light emitting diode and a silicon photo transistor.
 Power transistor and silicon transistor.

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