After dna replication is completed, after dna replication is completed, one dna double helix consists of two old strands and one dna double helix consists of two new strands each of the four dna strands consists of some old strand parts and some new strand parts there are four double helices each new dna double helix consists of one old dna strand and one new dna strand each new dna double helix consists of two new strands

Correct "each new DNA double helix consists of one old DNA strand and one new DNA strand"

When DNA replication takes place, the original DNA double helix is opened and new strands of DNA are built upon this opened DNA double helix creating, in the end, two DNA double helix - each with at least one original old DNA strand and a newly created DNA strand. The result two DNA double helix molecules that are hybrid in strands - one new and one old.