1. Select all of the true statements.
A. Pi is the area of a circle of radius 1.
B. Pi is the area of a circle of diameter 1.
C. Pi is the circumference of a circle of radius 1.
D. Pi is the circumference of a circle of diameter 1.
E. Pi is the constant of proportionality relating the diameter of a circle to its circumference.
F. Pi is the constant of proportionality relating the radius of a circle to its area.