Genetics Practice Help (Bio)

When a double stranded DNA molecule is heated, it denatures into two single stranded molecules.  The reason for that is that:

 A)    the proteins associated with the double helix are denatured and can no longer hold the DNA strands together
B)    the heat causes the helix to straighten, breaking the connections between the bases
C)    the heat breaks the hydrogen bonds holding the bases together in the centre of the molecule but does not affect the covalent bonds of the backbone
D)    the heat denatures the bases, preventing them from hydrogen bonding with each other.
E)    The heat causes the phosphate groups to ionize, preventing them from hydrogen bonding to the bases