Look at this on the psychrometric chart instead of describing it in words. Adiabatic drying moves the air state along a line of nearly constant wet bulb temperature, heading toward the saturation curve.
Along this line, as dry bulb temperature falls, the state point moves up and to the left, which is the direction of increasing humidity ratio \(W\). Since \(W = 0.622\dfrac{p_v}{P-p_v}\) at a fixed total pressure \(P\), a rising \(W\) means the vapour pressure \(p_v\) must also be rising.
Relative humidity is \(RH = \dfrac{p_v}{p_{ws}(T)} \times 100\), where \(p_{ws}(T)\) is the saturation vapour pressure at the current temperature. As \(T\) drops, \(p_{ws}\) drops too, while \(p_v\) is climbing. So the ratio \(RH\) climbs even faster than \(p_v\) alone would suggest.
All three quantities, humidity ratio, vapour pressure, and relative humidity, move in the same direction, up. That rules out any option that shows even one of them falling.
\[\boxed{\text{Humidity ratio, relative humidity and water vapour pressure all increase}}\]