The temperature of a point in space is given by $T=x^{2}+y^{2}-\mathrm{L}^{2} . \mathrm{A}$ mosquito located at $(1,1,0)$ desires to fly in such a direction that it will get heat as soon as possible then unit vector in direction the mosquito should fly is
(a) $\frac{\hat{i} \mid \hat{\hat{j}}}{\sqrt{2}}$
(b) $\frac{\hat{i} \mid \hat{j} \hat{k}}{\sqrt{3}}$
(c) $\frac{\hat{i}-\hat{j}}{\sqrt{2}}$
(d) $-\left(\frac{\hat{i}+\hat{j}}{\sqrt{2}}\right)$