What Is the Frequency Of $20 - \mathrm { mm }$

Multiple Choice

What is the frequency of $20 - \mathrm { mm }$ microwaves? $\left( c = 3.0 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s } \right)$

A) $15 \mathrm { GHz }$
B) $100 \mathrm { MHz }$
C) $400 \mathrm { MHz }$
D) $73 \mathrm { GHz }$