Mary has always been a sickly child. Her caring and devoted mother is always by her side. One week, Mary's mother leaves town to visit an old friend, and suddenly Mary starts to feel better. But, as soon as her mother returns, Mary starts to exhibit a host of unexplained symptoms yet again. Based on this observation, Mary's doctor worries that Mary's mother might have:

A. conversion disorder.
B. Munchausen syndrome.
C. Munchausen syndrome by proxy.
D. factitious disorder.