A laboratory sample obeys dtdT=k(T−18) with constant k. Which conclusion about k is most consistent with the fact that the sample’s temperature decreases toward 18∘C over time?
a) k>0, and a larger value of k produces slower cooling.
b) k<0, and a larger ∣k∣ produces faster cooling.
c) k<0, and a larger ∣k∣ produces slower cooling.
d) k<0, and a smaller ∣k∣ produces faster cooling.