D. Subjectivity over Objectivity. Truth is personal, not propositional or objective. There is no universe other than the universe of individual human subjectivity. There are no universals, only particulars. For the existentialist it was man's feelings and passion which made him a man.
Feelings are the standard for truth.
It is true if I feel strongly about it. Like all humanist philosophies existentialism contains within itself the seeds of its own destruction. The number one critique of existentialist philosophy is the inconsistency with which they live their lives. Current existentialists are likewise advocates of causes. Sartre himself seemed to admit this near his death.