Rembrandt's self-portraits ere created by the artists looking at himself in a mirror, and the painting and drawings therefore reverse his actual features. In the etchings the printing process creates a reversed image, and prints therefore show Rembrandt in the same orientation as he appeared to contemporaries.
A comedy is a form of play that has a happy and playful ending and a tragedy is a play where there is a fall in main characters or events that is disturbing.
While a mystery play is a form of drama based on the biblical events, and the miracle is a type of religious drama that is related to the life of the saints and martyrs of the middle ages.
The morality play is a form of drama that consists of the used popular legends in order to teach some morals through the allegory.
I believe the answer is d) Unity. Since unity is what makes all elements in an artwork combine together well-harmoniously, I would think that'd be the most significant principle of a design according to photography.