After gaining entry into the host cell by the zipper mechanism, the bacterium Listeria monocytogenes escapes phagosomes by secreting listeriolysin O. This protein …

A) is active at neutral pH and cannot be degraded by the proteasome.
B) is active at neutral pH and is rapidly degraded by the proteasome.
C) is active at acidic pH and cannot be degraded by the proteasome.
D) is active at acidic pH and is rapidly degraded by the proteasome.
E) is active at basic pH and cannot be degraded by the proteasome.