For a particular IC-fabrication process, the transconductance parameter k'n = 400 μA/V^2, and Vt = 0.5V. In an application in which VGS = VDS = Vsupply = 1.8V, a drain current (iD) of 2 mA is required of a device of minimum length (L) of 0.18 μm. What value of channel width must the design use (W), assuming saturation area?
A. 21 μm
B. 18 μm
C. 19 μm
D. 20 μm