For isolating a gene of long DNA molecules (50-100 KB) following is used:

Ans. A. Chromosome walking(Ref: Harper 30/e page463)Chromosome WalkingMethod to isolate and clone target DNA from a long segment of DNAIn Chromosome walking, a fragment representing one end of a long piece of DNA is used to isolate another fragment, that overlaps the first but extends the first. This process continued till the target DNA is isolated.Cystic fibrosis (CF) gene was the first to be isolated solely by chromosome walking.