If $\mathrm{a}, \mathrm{b}, \mathrm{c}$ are three distinct numbers in $\mathrm{AP}$ and $\mathrm{b}-\mathrm{a}, \mathrm{c}-\mathrm{b}$, a are in $\mathrm{GP}$, then a: b: $\mathrm{c}=$
(a) $2: 3: 1$
(b) $\frac{1}{2}: \frac{1}{3}: 1$
(c) $1: 2: 3$
(d) $2: 1: 6$