Because hydrogen bonds hold the two strands of a double-stranded DNA molecule together, the strands can be separated without breaking any covalent bonds. Every unique DNA molecule "melts" at a different temperature. In this context, Tm (melting temperature) is the point at which two strands separate, or become denatured. Order the DNA sequences listen below according to relative melting temperatures, from lowest Tm (easiest to denature) to highest Tm. Assume that they all begin as a stable double-stranded DNA molecules (complement not shown)
A. 5'- GGCGCACC- 3'
B. 5'- TATTGTCT-3'
C. 5'- GACTCCTG-3'
D. 5'-CTAACTGG-3'

A. (lowest Tm) B, D, C, A (highest Tm)
B. (lowest Tm) A, C, D, B (highest Tm)
C. (lowest Tm) C, D, A, B (highest Tm)
D. (lowest Tm) A, B, C, D (highest Tm)