The Fourth Amendment protects people against "unreasonable searches." Which is an example of the type of "unreasonable search" this amendment protects against?
A. A teacher asks a student to answer a hard question in front of the class.
B. A parent spends several hours trying to find a lost set of car keys.
C. A police officer looks through a student's backpack for no reason.
Determine the correct option from the provided choices and reply with its corresponding letter.

C