The stress-strain graph for a metal wire is as shown in the figure. In the graph, the region in which Hooke's law is obeyed, the ultimate strength and fracture points are represented by:(a) $\mathrm{OP}, \mathrm{R}, \mathrm{S}$
(b) $\mathrm{OQ}, \mathrm{S}, \mathrm{T}$
(c) $\mathrm{OP}, \mathrm{S}, \mathrm{T}$
(d) $\mathrm{OQ}, \mathrm{R}, \mathrm{S}$