Question 4If $a,b$ and $c$ are positive real numbers such that $$\frac a{a+b}=\frac{a+b}{a+b+c}=\frac c{b+c},$$ then $\dfrac ab$ equals$\frac{\sqrt{3}-1}{2}$1$\sqrt{2}$$\frac{1+\sqrt{5}}{2}$None of the above