Which of the following is true of hydrogen peroxide and carbamide peroxide as tooth bleaching agents?
a) Carbamide peroxide is three times stronger than hydrogen peroxide and has a shorter working time.
b) Hydrogen peroxide is three times stronger than carbamide peroxide and has a longer working time.
c) Hydrogen peroxide is three times stronger than carbamide peroxide and has a shorter working time.
d) Carbamide peroxide is three times stronger than hydrogen peroxide and has a longer working time.