Match each equation with its model.
(a) Exponential growth model
(i) $y=a e^{-b x}, b>0$
(b) Exponential decay model
(ii) $y=a+b \ln x$
(c) Logistic growth model
(iii) $y=\frac{a}{1+b e^{-r x}}$
(d) Gaussian model
(iv) $y=a e^{b x}, b>0$
(e) Natural logarithmic model
(v) $y=a+b \log _{10} x$
(f) Common logarithmic model
(vi) $y=a e^{-(x-b)^{2} / c}$