The Frictional Force of the Floor on a Large Suitcase $\theta$

The frictional force of the floor on a large suitcase is least when the suitcase is

A) pushed by a force parallel to the floor.
B) dragged by a force parallel to the floor.
C) pulled by a force directed at an angle $\theta$ above the floor.
D) pushed by a force directed at an angle $\theta$ into the floor.
E) turned on its side and pushed by a force parallel to the floor.