Which of these statements is not true for a temporary magnet?
a. the north pole of a temporary magnet will attract the south pole of a permanent magnet.
b. a temporary magnet can be made by rubbing iron with a strong magnet.
c. the field of a temporary magnet usually weakens over time.
d. the magnetic field of a temporary magnet does not loop from its north to its south pole.

Keeping in mind the life cycle of bacteriophages, consider the following problem: during the reproductive cycle of a temperate bacteriophage, the viral dna inserts into the bacterial chromosome where the resultant prophage behaves much like a trojan horse. it can remain quiescent, or it can become lytic and initiate a burst of progeny viruses. several operons maintain the prophage state by interacting with a repressor that keeps the lytic cycle in check. insults (ultraviolet light, for example) to the bacterial cell lead to a partial breakdown of the repressor, which in turn causes the production of enzymes involved in the lytic cycle. as stated in this simple form, would you consider this system of regulation to be operating under positive or negative control?