Help molecular biology lab....?

RNA is a single stranded macro-molecule with some intramolecular H-bonding (unpaired bases are looped out). DNA denaturation (by heating or extremes of pH) occurs less readily and the so-called melting out of the structure occurs over a short temperature spread (the midpoint of this is called Tm ot melting point). In contrast, RNA is readily denatured but since the presence of heterogeneous paired regions, RNA denaturation is spread over a wider temperature range than DNA, WHY?