b
For a particle in SHM, its speed depends on position as
$v=\omega \sqrt{A^{2}-x^{2}}$
Where $\omega$ is angular frequency and $A$ is amplitude Now $v ^{2}=\omega^{2} A ^{2}-\omega^{2} x ^{2}$
So, $\frac{ v ^{2}}{(\omega A )^{2}}+\frac{ x ^{2}}{( A )^{2}}=1$
So graph between $v$ and $x$ is elliptical