Select all of the true statements.

A. π is the area of a circle of radius 1
B. π is the area of diameter 1
C. π is the circumfrence of a circle of radius 1
D. π is the circumfrence of a circle of diameter 1
E. π is the constant of proportionality relating the diameter of a circle to its circumfrence
F. π is the constant of proportionality relating the radius of a circle to its area