Obtain the Thevenin and Norton equivalent circuits

Which of the following statements about equipment grounding conductors (EGCS) is true? A. The National Electrical Code permits the EGC to also perform as a grounding electrode conductor. B. More than one EGC must be used if multiple circuits are installed in a single raceway, cable, or cable tray. C. No current should be present in the EGC during normal operation. D. EGCs are required to be decreased in size to address voltage drop.

The contractor is controlled by?

Assuming all terminals are rated 75°C and you have a  #10 AWG THHN/THWN conductors in a conduit and the conduit is run on the roof off a office building where the ambient temperature never rises above 30°C the largest size circuit breaker or fuse permitted to protect these wires is:?

The wording that I am running into with questions such as "The number of conductors required to be installed between three-way and four-way switches is " is confusing.  The text is not expalining this in a way that I am understanding anything other than grounding conductor, which is optional unless I am using a metal box.  So what type of "conductor" is beng discussed?

Please answer in typing format