Which of the following statements$)$ is $/$ are false?

$$ a$.$ An entity can be either a source or a destination.

$$ c$.$ A context diagram depicts a data processing system and the external entities that are the sources and destinations of the system's inputs and outputs.

$$ d$.$ Level $0$ and Level $1$ DFDs may show more than one process, labeled in sequence and subdivided.

$$ e$.$ Both directional and bi$-$directional arrows must be used in each level of a DFDs$.$

$$ b$.$ Lower level DFDs show physical storage mediums $($such as files$)$ used to store the data.