Answer: c. Milwaukee
Step-by-step explanation:
The warmer the air gets, the higher its capacity for water vapor. Thus, the relative humidity would increase as the dew point temperature decreases and vice versa. The relative humidity is usually highest at sunrise at the point when the overnight low temperature is usually close to the dew point.
Since Milwaukee has the lowest Td = 21°F and its R.H = 51.358, a value higher than the rest since the rest have negative values.