The triangle formed by the tangent to the parabola $y=x^{2}$ at the point $x=x_{0}\left(x_{0} \in[1,2]\right)$ the y-axis and the straight line $\mathrm{y}=\mathrm{x}_{0}{ }^{2}$ has the greatest area if $\mathrm{x}_{0}=$
(a) 1
(b) $\frac{4}{3}$
(c) $\frac{3}{2}$
(d) 2