A parasite which becomes saprophytic in the absence of host is called: 

Parasites are the kind of organisms that depend on the host organism for their sustenance. They mostly negatively affect their host and can also cause several diseases. 

Parasites can be further divided based on their dependence on their hosts. Some parasites can exist without a host's presence and become parasitic when the host is available. Such parasites are called facultative parasites. When these parasites do not have access to a host, they become saprophytic. Saprophytes are the kind of organisms that feed on dead and decaying matter. 

Therefore the correct answer would be facultative parasites.

Hence the correct answer is option B.