The correct answer is: A. In header course.
A queen closer is a brick that is cut to be half the length of a standard brick. It is used to fill in the space between two headers in a header course. A header course is a course of bricks that are laid on edge, perpendicular to the face of the wall.
A stretcher course is a course of bricks that are laid flat, parallel to the face of the wall. A stretcher course next to the first brick would be a course of bricks that is laid flat, parallel to the face of the wall, and that is immediately adjacent to the first course of bricks in the wall.
A queen closer cannot be placed in a stretcher course because it is too short. It also cannot be placed in a stretcher course next to the first brick because it would not be able to fit between the first course of bricks and the second course of bricks.
A queen closer can be placed in a header course because it is the correct length to fit between two headers. It can also be placed in a header course next to the first brick because it would be able to fit between the first course of bricks and the second course of bricks.