Answer:
The virus will transfer the DNA encoding cholera toxin to the next bacteria it infects, which will make that bacteria cholera-causing.
Explanation:
The process described in this question is a kind of gene transfer in bacteria called TRANSDUCTION. Transduction is the transfer of fragments of DNA from one bacterium to another via a virus called bacteriophage.
As stated in this question, the virus (bacteriophage) infects a cholera-causing bacterium. The bacteriophage moves from lysogenic cycle to lytic cycle and includes some pieces of the bacterial DNA, which encodes information for making the cholera toxin, in its own genome.
This means that the cholera-making toxin DNA is now a part of the virus's genome and hence, will transfer it to the next bacteria it infects in a process called TRANSDUCTION. This will make that bacteria a cholera causing bacteria.
I do believe that it is C. crossing over :) I hope that is correct, it seems like the only plausible answer.
She could use a control to compare her data to and make sure it is cleaner. Ex. Use the old detergent on ten shirts and then use the new detergent on another ten shirts. She would then compare the shirts she did each detergent on and come up with her conclusion.
B. I think I'm not so sure but that's my best guess.