If $A+B=\large\frac{\pi}{3}$ where $A,B\in R^+$ then the minimum value of $\sec A+\sec B$ is equal to

Question

$(a)\;\large\frac{2}{\sqrt 3}\qquad$$(b)\;\large\frac{4}{\sqrt 3}$$\qquad(c)\;2\sqrt 3\qquad(d)\;None\;of\;these$