Bacteria were cultured in a medium that contained $^{15}\text{N}$. After a number of generations, every DNA molecule contained $^{15}\text{N}$. Some of these bacteria were then moved into a medium containing the usual nitrogen isotope, $^{14}\text{N}$. They were permitted to divide once. The DNA from some of these bacteria was removed and examined. It was entirely hybrid DNA, with equal proportions of $^{14}\text{N}$ and $^{15}\text{N}$. The rest of the bacteria were kept in the $^{14}\text{N}$ medium and allowed to divide once again. The DNA from some of these bacteria was then extracted and analysed. What is the composition of this DNA?
- A25% hybrid DNA
- B50% hybrid DNA
- C75% hybrid DNA
- D100% hybrid DNA