Which of the Following Is Not Considered Lawful Under the Plain

Which of the following is not considered lawful under the plain view rule permitting warrantless searches?

A) A police officer looking at a field that is surrounded by a barbed wire fence upon which are posted several "No Trespassing" signs sees a large number of marijuana plants being cultivated in the field.
B) While executing a search warrant authorizing him to search a house for drugs, a police officer observes some stolen property.
C) A police officer who is conducting a legal search for illegal drugs moves a desktop computer to locate its serial number.
D) A police officer pulls a vehicle over for running a red light and observes a quantity of illegal drugs in the back seat.