80. Which of the following statements for thermal denatuation of DNA are false?1. The absorption of ultraviolet at 260 nm increases.2.The DNA helical structure unwinds. 3. The covalent N-glycosidic bond between the base and the deoxyribose breaks. 4.The melting temperature of DNA with 60% A+T content is lower than that with 20% G+C content. 5.The double-helical DNA becomes single-stranded DNA at melting temperature. (A)135(B)134(C)145(D)234(E)345