A dart board has a diameter of 40 cm and is divided into 20 congruent sectors. What is the area of one of the sectors?

A. 20 [tex] \pi [/tex] cm²
B. 40 [tex] \pi [/tex] cm²
C. 80 [tex] \pi [/tex] cm²
D. 800 [tex] \pi [/tex] cm²