You can change your grade by going to your profile in the top right corner.
Depends on how you wanna do it, through iTunes or whatever other you are syncing from
There is probably a loose or broken cable, most likely connected to the hard drive
The correct answer is B, a laminated core and a shading coil.
A key difference in an AC relay is the presence of a "shading coil". The purpose of this coil is to keep the relay on when the current drops to zero during phase change (note that in AC power the current and voltage are alternating in a sine wave around 50/60 times per second). The shading coil retains some magnetic energy and essentially holds the relay ON when the current drops to zero momentarily due to the AC waveform.
AC relays also have a laminated core to prevent losses due to eddy current heating.
