Which one of the following is the Young's modulus (in $N/m^2$) for the wire having the stress-strain curve shown in the figure?

The strain-stress curves of three wires of different materials are shown in the figure. $P, Q$ and $R$ are the elastic limits of the wires. The figure shows that

In the given stress-strain graph,what does point $D$ indicate?

The diagram shows the stress versus strain curve for materials $A$ and $B$. From the curves,we infer that:

The stress-strain graphs for materials $A$ and $B$ are shown in the figure. The graphs are drawn to the same scale.
$(a)$ Which of the materials has the greater Young's modulus?
$(b)$ Which of the two is the stronger material?

The figure shows the stress-strain curve for a given material. What are $(a)$ Young's modulus and $(b)$ approximate yield strength for this material?