$17.$

The dew point temperature lines on psychrometric charts are straight inclined sloping downwards to the right. When relative humidity of moist air is $100\%,$ then

wet bulb temperature$=$dry bulb temperature.

wet bulb temperature$=$dew point temperature.

saturation temperature$=$dew point temperature.

all $\text{'}$a$\text{'},\text{'}$b$\text{'}$ & $\text{'}$c$\text{'}$