GFCI circuitry constantly checks for difference in current between a ground and neutral b hot and neutral c hot and ground?

GFCI's monitor current in the hot and neutral wires to make sure they match. If they don't, it's considered a ground fault, and the GFCI trips. However: If you're taking this test, you're being tested on your electrical knowledge, the strength of which may cost someone their life one day. It's not about homework or test questions, but you're asking a homework or test question in a trade dangerous enough for people to need licenses. ----

If you do not understand the work well enough to accomplish it yourself properly and safely, don't try it. Consult a professional electrician, as they are proficient enough to do it properly and safely. When working on electrical circuits and equipment, make sure to de-energize the circuit you will be working on. Then test the circuit with a definitive means to make sure it is off (multimeter with metal tipped leads, voltage tester with metal tipped leads, etc., not a non-contact tester, which is non-definitive.)