Let $f:R\to R$ be such that $f(1)=3$ and $f'(1)=6$.Then $\lim\limits_{x\to 0}\bigg[\large\frac{f(1+x)}{f(1)}\bigg]^{1/x}$ equals

Question

$(a)\;1\qquad(b)\;e^{1/2}\qquad(c)\;e^2\qquad(d)\;e^3$