Final answer:
The legal burden of proof necessary to obtain a search warrant is 'probable cause', as established by the Fourth Amendment of the U.S. Constitution. The correct option is (A).
Step-by-step explanation:
The legal burden of proof required to obtain a search warrant is probable cause.
This standard is established by the Fourth Amendment of the United States Constitution, which states that "no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
Probable cause serves as the legal justification for a search or seizure and is a lower threshold than reasonable suspicion, beyond a reasonable doubt, or preponderance of the evidence, which are standards used in other legal contexts.