Final answer:
In data flow diagrams, two parallel lines symbolize a data store, which depicts where data is kept in a system.
The answer is option ⇒b
Step-by-step explanation:
The symbol in data flow diagrams (DFD) that is represented by two parallel lines is the b. data store. This symbol is used to depict where data is stored within a system, such as a database or a filing cabinet.
In a DFD, data flows are represented by arrows, external entities by squares or rectangles, and internal entities or processes by circles or rounded rectangles.
The answer is option ⇒b