Which of the Below Situations Would Be Considered as a Search

Which of the below situations would be considered as a search under the Fourth Amendment?

A) The examining the contents of garbage can that is on a street curb for pickup.
B) Police officer looking into the truck bed of a pickup parked in a store parking lot.
C) Opening the trunk of a car that was stopped for speeding without the owner's consent.
D) Investigating the crops being grown in the fields of a local farmer.