The correct option is C When d ln KdT<0, the reaction is exothermic
In van 't Hoff's Equation
d ln KdT=ΔH∘RT2
or, ln K=−ΔH∘R1T+C
This is a linear equation so the slope is constant throughout.
The slope of the graph would depend on the sign of ΔH and it can be negative or positive if the reaction is endothermic or exothermic respectively.