Engine 2014: Electricity

1. A supply alternate logic levels at the input(s) and test for  change of state conditions at the output
2. B ground all inputs and test for a logic "1" at the output
3. C open all inputs and test for a logic '0' at the output
4. D vary each input smoothly from 0-10 volts and test for similar variance at the output

Tip: press A-D to answer