A technician testing a logic circuit sees that the output of a particular INVERTER is stuck LOW while its input is pulsing. Which one of the…

A technician testing a logic circuit sees that the output of a particular INVERTER is stuck LOW while its input is pulsing. Which one of the following is the possible reason for this faulty operation?

1. a) The output of the INVERTER is internally grounded
2. b) The output of the INVERTER is externally grounded
3. c) The input being driven by output of the INVERTER is internally grounded
4. d) All of the above