The Figure Below Depicts Changes to the Amount of DNA

The figure below depicts changes to the amount of DNA present in a recipient cell that is engaged in conjugation with an Hfr cell. Hfr cell DNA begins entering the recipient cell at Time A. Assume that reciprocal crossing over occurs (in other words, a fragment of the recipient's chromosome is exchanged for a homologous fragment from the Hfr cell's DNA) . Use this figure to answer the following questions.

-Which question, arising from the results depicted in the above figure, is most interesting from a genetic perspective, and has the greatest potential to increase our knowledge base?

A) If reciprocal crossing over could occur even if the piece of donated Hfr DNA were identical to the homologous portion of the recipient's chromosome, what prevents this from occurring?
B) What forces are generally responsible for disrupting the sex pilus?
C) How is it that a recipient cell does not necessarily become an Hfr cell as the result of conjugation with an Hfr cell?
D) What makes a cell an Hfr cell?