Why Must a Shuttle Vector Possess Two Origins of Replication

Why must a shuttle vector possess two origins of replication instead of one?

A) Shuttle vectors must replicate in multiple hosts with each host requiring a different origin.
B) Shuttle vectors must be able to replicate from two different origins of replication depending upon the specific growth conditions.
C) Shuttle vectors only have one origin of replication,not two.
D) Shuttle vectors use one origin for replication and the other origin for shuttling recombinant DNA into new hosts.