Your Friend Took an Introductory Statistics Class Last Year and Learned

Your friend took an introductory statistics class last year and learned all about density curves. She tells you that two requirements of a density curve are:

A) the curve is always above the horizontal axis, and the area under the curve is one.
B) the curve is always above the horizontal axis, and the curve is symmetric.
C) the area above the horizontal axis must be larger than one if there is any area below the axis.
D) the area below the curve and above the horizontal axis must exceed one.