Question

which enzyme is responsible for creating the covalent bonds that connect the sugar phosphate backbone of the new DNA molecules

Answer 1

Ligase

Answer 2

Hmm. I am not sure exactly which part of the whole DNA replication process the question refers to. Ligase is only used in a very particular spot, after the the RNA primer is replaced with DNA at the end of replication ligase connects the primer to the rest of the strand. For most of replication a polymerase is what adds nucleotides. Though the question may be asking what enzyme builds the individual nucleotides.