What Is the Purpose of a Faraday Bag

What is the purpose of a Faraday bag?

A) To hold law enforcement field devices until they are ready to be used. Failure to properly secure such forensic devices may result in compromised evidence gathering capabilities
B) The long-term storage of ready-access memory to facilitate long term storage of digital evidence
C) To scrub a hard disc drive of sensitive information before being disposed of after an investigation
D) To prevent an electronic device from being accessed and augmented remotely