What is required to transfer a firearm in Washington?

In Washington, it is required by law for all firearm transfers to undergo a background check. This applies to all types of transfers, whether through a licensed dealer or a private sale. Therefore, options A, C, and D are incorrect because they are missing the important step of a background check. A bill of sale is not enough to legally transfer a firearm in Washington. Additionally, while a concealed pistol license (CPL) can allow the owner to carry a loaded handgun in public, it is not a substitute for a background check when transferring a firearm. Therefore, the correct answer is B.