Question $7[3$ marks$]$ For a low$-$cost $4416-$key numeric keypad, to find out which key is being pressed, one can A$.$ Multiply each vertical column value by each horizontal row value to find the appropriate LOW that indicates the intersection B$.$ Press the hash $($#$)$ key after pressing a number or letter key to complete the sequence C$.$ Take each of the vertical columns LOW in turn, leaving the other columns HIGH, and read each horizontal row to find a LOW D$.$ Wire the outputs from the keypad directly to a seven$-$segment display to see the value Question $8[3$ marks$]$ A zero$-$level calibration needs to be carried out for a Hall effect sensor to A$.$ Ensure that a zero value will be read for no external magnetic field B$.$ Allow a south pole magnetic field to be detected by a positive value C$.$ Allow a north pole magnetic field to be detected by a negative value D$.$ All of the above