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.