When DNA replication starts

Okazaki fragments are produced on lagging strand. DNA replication starts with unwinding of DNA duplexes which are held together by hydrogen bond. Helicases move along the double stranded DNA and separate the strands by breaking hydrogen bonds between base pairs. ATP hydrolysis provides the required energy for breaking of hydrogen bonds.  DNA polymerase enzyme adds deoxyribonucleotides to primer by formation of phosphodiester bond betweenbetween the 3' oxygen of a growing strand and alpha phosphate of a dNTP.  Breaking of bond between nitrogen base and deoxyribose sugar is part of nucleotide catabolism; it does not occurs during DNA replication. Thus, the correct answer is option B.