acdc.

alternating current means the current direction is changed as the current flow

main electricity 會用a.c is because
1. the generator primarily have a.c. output
2. the far distance transfer needs step-up the voltage, transformer have to be used, it works for a.c. only
如果用d.c 會點
1.cannot transfer far away from the generator
2. many applicants do not work

load is the part that consume energy..e.g. bulb, resistor
NOT the battery basically ( although battery have resistance and spend a little energy)