The Bio?lm That Forms in Your Shower ("Shower Curtain Scum")

The bio?lm that forms in your shower ("shower curtain scum") can tolerate exposure to hot water when you shower and is resistant to desiccation between showers. The microbes in the bio?lm are not endospores, so what is the best explanation for their survival under these conditions?

A) Bio?ms are composed of diverse microbes, and within each bio?lm, there are certain to be endospore-formers and thermophiles.
B) Although some microbes will be killed, those embedded deeply within the bio?lm are protected from environmental challenges.
C) The shower hasn't been thoroughly cleaned in a while, and when I really scrub it, the microbes will all be killed.
D) Dead skin cells continuously replenish the bio?lm, and organic soaps provide a continuous carbon source.