Engine 2014: Electricity

1. A before using the probe each time for detecting the presence of and verifying the absence of voltage only
2. B after using the probe each time for detecting the presence of and verifying the absence of voltage only
3. C before and after using the probe each time for detecting the presence of and verifying the absence of voltage only
4. D whenever it is suspected that the probe is not accurately detecting the presence of voltage

Tip: press A-D to answer