The circumference of a circle is 42pie cm. Find the diameter, the radius, and the length of an arc of 90 degrees.

A. 42 cm; 84cm; 5.3pie cm.
B. 21 cm; 42 cm; 5.3pie cm.
C. 42 cm; 21 cm; 10.5pie cm.
D. 84 cm; 21 cm; 135pie cm.